IN  MEMOR1AM 
BERNARD  MOSES 


.  :?.£ 


3-v 


33- 


LIGHT   SCIENCE  FOR 
LEISURE  HOURS. 


A  SERIES  OF  FAMILIAR   ESSAYS   ON  SCIENTIFIC 
SUBJECTS,  NATURAL  PHENOMENA,  ETC. 


BY 

RICHARD  A.  PROCTOR,  B.  A.  CAMB.,  F.  R.  A.  S. 

M 

AUTHOR  OF 
"THE  SUN,"  "OTHER  WORLDS  THAN  OURS,"  "SATURN,"  ETC. 


"  I  bear  you  witness  as  ye  bear  to  me, 

Time,  day,  nigH  sun,  stars,  life,  death,  a^  sea,  earth." 

"  **,  *  -,'   \  -      SWINBURNE. 


NEW  YORK : 

D.     APPLETON    AND    COMPANY, 

549   &  551   BROADWAY. 

1871. 


Oil  I 


BERNARD 


PREFACE. 


THE  Essays  in  the  present  volume  have  been  selected 
from  my  contributions  to  serial  literature  during  the 
past  three  or  four  years.  Although  I  have  for  some 
time  been  urged  to  publish  such  a  volume,  I  think 
I  should  not  have  ventured  to  do  so  but  for  the 
kindness  with  which  my  "  Other  "Worlds  "  and  "  The 
Sun  "  have  been  received,  both  by  the  press  and  the 
public. 

In  preparing  these  Essays,  my  chief  object  has  been 
to  present  scientific  truths  in  a  light  and  readable 
form — clearly  and  simply,  but  with  an  exact  adherence 
to  the  facts  as  I  see  them.  I  have  followed — here  and 
always — the  rule  of  trying  to  explain  my  meaning 
precisely  as  I  should  wish  others  to  explain,  to  my- 
self, matters  with  which  I  was  unfamiliar.  Hence  I 
have  avoided  that  excessive  simplicity  which  some 
seem  to  consider  absolutely  essential  in  scientific  essays 
intended  for  general  perusal,  but  which  is  often  even 
more  perplexing  than  a  too  technical  style.  The  chief 


887302 


4  PREFACE. 

rule  I  have  followed,  in  order  to  make  my  descriptions 
clear,  lias  been  to  endeavor  to  make  eacli  sentence 
bear  one  meaning,  and  one  only.  Speaking  as  a 
reader,  and  especially  as  a  reader  of  scientific  books,  I 
venture  to  express  an  earnest  wish  that  this  simple 
rule  were  never  infringed,  even  to  meet  the  require- 
ments of  style. 

It  will  hardly  be  necessary  to  mention  that  several 
of  the  shorter  Essays  are  rather  intended  to  amuse 
than  to  instruct. 

The  Essay  on  the  influence  which  marriage  has 
been  supposed  to  exert  on  the  death-rate  is  the  one 
referred  to  by  Mr.  Darwin  at  page  176  (vol.  i.)  of  his 
"Descent  of  Man." 

This  and  the  other  Essays  from  the  Daily  News 
are  selected  from  a  large  number  of  articles  which 
I  wrote  in  the  years  1868-'TO.  It  was  by  my  kind 
friend  Mr.  Walker,  formerly  editor  of  the  Daily  News, 
that  I  was  first  urged  to  collect  my  Essays  into  a 
volume.  I  have  to  thank  the  proprietors  and  the 
present  editor  of  the  Daily  News,  and  the  proprietors 
and  editors  of  the  other  journals  from  which  the  pres- 
ent series  has  been  selected,  for  freely  according  me 
permission  to  reprint  these  Essays. 

RICHARD  A.  PROCTOR. 

LONDON,  May,  1871. 


CONTENTS. 


PAGB 

STRANGE  DISCOVERIES  RESPECTING  THE  AURORA,      ...         7 
THE  EARTH  A  MAGNET,  .....  28 

OUR  CHIEF  TIMEPIECE  LOSING  TIME,  .  .  .  .45 

ENCKE,  THE  ASTRONOMER,          .....  62 

VENUS  ON  THE  SUN'S  FACE,  .  .  .  .  .66 

RECENT  SOLAR  RESEARCHES,      .  .  .  .  .  91 

GOVERNMENT  AID  TO  SCIENCE,         .  .  .  .  .98 

AMERICAN  ALMS  FOR  BRITISH  SCIENCE,  .  .  .  102 

THE  SECRET  OF  THE  NORTH  POLE,    .....      109 

Is  THE  GULF  STREAM  A  MYTH?  .  .  .  .  129 

FLOODS  IN  SWITZERLAND,      .  .  .  •  .  .150 

A  GREAT  TIDAL  WAVE,  .  .  .  .  .155 

DEEP-SEA  DREDGINGS,  .  .  .  .  .  .160 

THE  TUNNEL  THROUGH  MONT  CENIS,     .  .  .  .  166 

TORNADOES,    .  .  .  .  .  .  .  .171 

VESUVIUS,          .  .  .  .  .  .  ,  186 

THE  EARTHQUAKE  IN  PERU,  .....     209 

THE  GREATEST  SEA-WAVE  EVER  KNOWN,  .  .  .  216 

THE  USEFULNESS  OP  EARTHQUAKES,  ....     233 


6  CONTENTS. 

PAGH 

THE  FORCING  POWER  OF  RAIN,  ....  248 

A  SHOWER  OF  SNOW-CRYSTALS,        .....  254 

LONG  SHOTS,      .......  256 

INFLUENCE  OF  MARRIAGE  ON  THE  DEATH-RATE,       .  .  .  262 

THE  TOPOGRAPHICAL  SURVEY  OF  INDIA,  .  .  .  269 

A   SHIP  ATTACKED   BY   A   SwORD-FlSH,  .  .  .  .281 

THE  SAFETY-LAMP,         .            .            .            .            .            .  284 

THE  DUST  WE  HAVE  TO  BREATHE,   .....     290 

PHOTOGRAPHIC  GHOSTS,  ......  293 

THE  OXFORD  AND  CAMBRIDGE  ROWING  STYLES,       .            .  .     295 

BETTING  ON  HORSE-RACES;   OR  THE  STATE  OF  THE  ODDS,        .  301 

SQUARING  THE  CIRCLE,         .            .            .           .            .  .315 

A  NEW  THEORY  OF  ACHILLES'S  SHIELD,           .            .            .  324 


LIGHT    SCIENCE 
FOE   LEISUEE    HOUES. 


STRANGE  DISCOVERIES  RESPECTING 
THE  AURORA. 

ONE  of  the  most  mysterious  and  beautiful  of 
Nature's  manifestations  promises  soon  to  disclose  its 
secret.  The  brilliant  streamers  of  colored  light  which 
wave  at  certain  seasons  over  the  heavens  have  long 
since  been  recognized  as  among  the  most  singular  and 
impressive  of  all  the  phenomena  which  the  skies  pre- 
sent to  our  view.  There  is  something  surpassingly  beau- 
tiful in  the  appearance  of  the  true  "  auroral  curtain." 
Fringed  with  colored  streamers,  it  waves  to  and  fro  as 
though  shaken  by  some  unseen  hand.  Then  from  end 
to  end  there  pass  a  succession  of  undulations,  the  folds 
of  the  curtain  interwrapping  and  forming  a  series  of 
graceful  curves.  Suddenly,  and  as  by  magic,  there 
succeeds  a  periecc  stillness,  as  though  the  unseen 
power  which  had  been  displaying  the  varied  beauties 
of  the  auroral  curtain  were  resting  for  a  moment.  But 


8  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

even  while  the  motion,  of  the  curtain  is  stilled  we  see 
its  light  mysteriously  waxing  and  waning.  Then  as 
we  gaze,  fresh  waves  of  disturbance  traverse  the  magic 
canopy.  Startling  coruscations  add  splendor  to  the 
scene,  while  the  noble  span  of  the  auroral  arch  from 
which  the  waving  curtain  seems  to  depend,  gives  a 
grandeur  to  the  spectacle  which  no  words  can  ade- 
quately describe.  Gradually,  however,  the  celestial 
fires  which  have  illuminated  the  gorgeous  arch  seem  to 
die  out.  The  luminous  zone  breaks  up.  The  scene 
of  the  display  becomes  covered  with  scattered  streaks 
and  patches  of  ashen  gray  light,  which  hang  like 
clouds  over  the  northern  heavens.  Then  these  in  turn 
disappear,  and  nothing  remains  of  the  brilliant  specta- 
cle but  a  dark  smoke-like  segment  on  the  horizon. 

Such  is  the  aurora  as  seen  in  arctic  or  antarctic 
regions,  where  the  phenomenon  appears  in  its  fullest 
beauty.  Even  in  our  own  latitudes,  however,  strik- 
ingly beautiful  auroral  displays  may  sometimes  be 
witnessed.  Yet  those  who  have  seen  the  spectacle 
presented  near  the  true  home  of  the  aurora,  recognize 
in  other  auroras  a  want  of  the  fulness  and  splendor  of 
color  which  form  the  most  striking  features  of  the 
arctic  and  antarctic  auroral  curtains. 

Hitherto  the  nature  of  the  aurora  has  been  a 
mystery  to  men  of  science  ;  nor,  indeed,  does  the  dis- 
covery we  are  about  to  describe  throw  even  now  full 
light  on  the  character  of  the  phenomenon.  That  dis- 


THE  AURORA.  9 

covery,  however,  affords  promise  of  a  speedy  solution 
of  the  perplexing  problems  presented  by  auroral  dis- 
plays; and  in  itself,  it  is  so  full  of  interest  and  so 
suggestive,  that  our  physicists  already  recognize  it  as 
one  of  the  most  important  which,  have  been  made  in 
recent  times. 

A  few  brief  words  in  explanation  of  the  progress 
which  had  been  effected  in  the  study  of  auroral  phe- 
nomena, will  serve  to  render  the  interest  and  impor- 
tance of  the  discovery  we  have  to  describe  more 
apparent. 

Let  it  be  premised,  then,  that  physicists  had  long 
since  recognized  in  the  aurora  a  phenomenon  of  more 
than  local,  of  more  even  than  terrestrial,  significance. 
They  had  learned  to  associate  it  with  relations  which 
affect  the  whole  planetary  scheme.  Let  us  inquire 
how  this  had  come  about. 

So  long  as  men  merely  studied  the  appearances  pre- 
sented by  the  aurora,  so  long  in  fact  as  they  merely 
regarded  the  phenomenon  as  a  local  display,  they  could 
form  no  adequate  conception  of  its  importance.  The 
circumstance  which  first  revealed  something  of  the  true 
character  of  the  aurora  was  one  which  seemed  to 
promise  little. 

Arago  was  engaged  in  watching  from  day  to  day, 
and  from  year  to  year,  the  vibrations  of  the  magnetic 
needle  in  the  Paris  Observatory.  He  traced  the 
slow  progress  of  the  needle  to  its  extreme  westerly 


10  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

variation,  and  watched  its  course  as  it  began  to  retrace 
its  way  toward  the  true  north.  He  discovered  the 
minute  vibration  which  the  needle  makes  each  day 
across  its  mean  position.  He  noticed  that  this  vibra- 
tion is  variable  in  extent ;  and  so  he  was  led  to, watch 
it  more  closely.  Thus  he  had  occasion  to  observe 
more  attentively  than  had  yet  been  done  the  sudden 
irregularities  which  occasionally  characterize  the  daily 
movements  of  the  needle. 

All  this  seems  to  have  nothing  to  do  with  the 
auroral  streamers ;  but  we  now  reach  the  important 
discovery  which  rewarded  Arago's  patient  watch- 
fulness. 

In  January,  1819,  he  published  a  statement  to  the 
effect  that  the  sudden  changes  of  the  magnetic  needle 
are  often  associated  with  the  occurrence  of  an  aurora. 
I  give  the  statement  in  his  own  words,  as  translated 
by  General  Sabine :  "  Auroras  ought  to  be  placed  in 
the  first  rank  among  the  causes  which  sometimes  dis- 
turb the  regular  march  of  the  diurnal  changes  of  the 
magnetic  needle.  These  do  not,  even  in  summer, 
exceed  a  quarter  of  a  degree,  but  when  an  aurora 
appears,  the  magnetic  needle  is  often  seen  to  move  in 
a  few  instants  over  several  degrees."  "During  an 
aurora,"  he  adds,  "one  often  sees  in  the  northern 
region  of  the  heavens  luminous  streamers  of  different 
colors  shoot  from  all  points  of  the  horizon.  The 
point  in  the  sky  to  which  these  streamers  converge  is 


THE  AURORA.  11 

precisely  the  point  to  which  a  magnetized  needle  sus- 
pended by  its  centre  of  gravity  directs  itself. 

It  has,  moreover,  been  shown  that  the  concentric 
circular  segments,  almost  similar  in  form  to  the  rain- 
bow, which  are  usually  seen  previous  to  the  appearance 
of  the  luminous  streamers,  have  their  two  extremities 
resting  on  two  parts  of  the  horizon  which  are  equally 
distant  from  the  direction  toward  which  the  needle 
turns  ;  and  the  summit  of  each  arc  lies  exactly  in  that 
direction.  From  all  this  it  appears,  incontestable/,  that 
there  is  an  intimate  connection  between  the  causes  of 
auroras  and  those  of  terrestrial  magnetism" 

This  strange  hypothesis  was,  at  first,  much  opposed 
by  scientific  men.  Among  others  the  late  Sir  David 
Brewster  pointed  out  a  variety  of  objections,  some  of 
which  appeared  at  first  sight  of  great  force.  Thus,  he 
remarked  that  magnetic  disturbances  of  the  most 
remarkable  character  have  often  been  observed  when 
no  aurora  has  been  visible ;  and  he  noticed  certain 
peculiarities  in  the  auroras  observed  near  the  polar 
regions,  which  did  not  seem  to  accord  with  Arago's 
view. 

But  gradually  it  was  found  that  physicists  had  mis- 
taken the  character  of  the  auroral  display.  It  ap- 
peared that  the  magnetic  needle  not  only  swayed 
responsively  to  auroras  observable  in  the  immediate 
neighborhood,  but  to  auroras  in  progress  hundreds  or 
even  thousands  of  miles  away.  Nay,  as  inquiry  pro- 


12  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

grossed,  it  was  discovered  that  the  needles  in  our 
northern  observatories  are  swayed  by  influences  asso- 
ciated even  with  the  occurrence  of  auroras  around  the 
southern  polar  regions. 

In  fact,  not  only  have  the  difficulties  pointed  out 
(very  properly,  it  need  hardly  be  remarked)  by  Sir 
David  Brewster  been  wholly  removed  ;  but  it  has  been 
found  that  a  much  closer  bond  of  sympathy  exists 
between  the  magnetized  needle  and  the  auroral 
streamers  than  even  Arago  had  supposed.  It  is  not 
merely  the  case  that  while  an  auroral  display  is  in 
progress  the  needle  is  subject  to  unusual  disturbance, 
but  the  movements  of  the  needle  are  actually  synchro- 
nous with  the  waving  movements  of  the  mysterious 
streamers.  An  aurora  may  be  in  progress  in  the  north, 
of  Europe,  or  even  in  Asia  or  America,  and  as  the 
colored  banners  wave  to  and  fro,  the  tiny  needle, 
watched  by  patient  observers  at  Greenwich  or  Paris, 
will  respond  to  every  phase  of  the  display. 

And  I  may  notice  in  passing  that  two  very  inter- 
esting conclusions  follow  from  this  peculiarity  :  First, 
every  magnetic  needle  over  the  whole  earth  must  be 
simultaneously  disturbed;  and,  secondly,  the  auroral 
streamers  which  wave  across  the  skies  of  one  country, 
must  move  synchronously  with  those  which  are  visible 
in  the  skies  of  another  country,  even  though  thousands 
of  miles  may  separate  the  two  regions. 

But  I  must  pass  on  to  consider  further  the  circum- 


THE  AURORA.  13 

stances  which  give  interest  and  significance  to  the 
strange  discovery  which  is  the  subject  of  this  paper. 

Could  we  only  associate  auroras  with  terrestrial 
magnetism,  we  should  still  have  done  much  to  enhance 
the  interest  which  the  beautiful  phenomenon  is  calcu- 
lated to  excite.  But  when  once  this  association  has 
been  established,  others  of  even  greater  interest  are 
brought  into  recognition.  For  terrestrial  magnetism 
has  been  clearly  shown  to  be  influenced  directly  by  the 
action  of  the  sun.  The  needle  in  its  daily  vibration 
follows  the  sun,  not  indeed  through  a  complete  revolu- 
tion, but  as  far  as  the  influence  of  other  forces  will  per- 
mit. This  has  been  abundantly  confirmed,  and  is  a 
fact  of  extreme  importance  in  the  theory  of  terrestrial 
magnetism.  Wherever  the  sun  may  be,  either  on  the 
visible  heavens  or  on  that  half  of  the  celestial  sphere 
which  is  at  the  moment  beneath  the  horizon,  the  end 
of  the  needle  nearest  to  the  sun  makes  an  effort  (so  to 
speak)  to  point  more  directly  toward  the  great  ruling 
centre  of  the  planetary  scheme.  Seeing,  then,  that  the 
daily  vibration  of  the  needle  is  thus  caused,  we  recog- 
nize the  fact  that  the  disturbances  of  the  daily  vibra- 
tion may  be  referred  to  some  peculiarity  of  the  solar 
action. 

It  was  not,  therefore,  so  surprising  as  many  have 
supposed,  that  the  increase  and  diminution,  of  these 
disturbances,  in  a  period  of  about  eleven  years,  should 
be  found  to  correspond  with  the  increase  and  diminu- 


14  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

tion  of  the  number  of  solar  spots  in  a  period  of  equal 
length. 

"We  already  begin  to  see,  then,  that  auroras  are 
associated  in  some  mysterious  way  with  the  action  of 
the  solar  rays.  The  phenomenon  which  had  been 
looked  on  for  so  many  ages  as  a  mere  spectacle,  caused 
perhaps  by  some  process  in  the  upper  regions  of  the 
air,  of  a  simply  local  character,  has  been  brought  into 
the  range  of  planetary  phenomena.  As  surely  as 
the  brilliant  planets  which  deck  the  nocturnal  skies 
are  illuminated  by  the  same  orb  which  gives  us  our 
days  and  seasons,  so  are  they  subject  to  the  same  mys- 
terious influence  which  causes  the  northern  banners  to 
wave  resplendently  over  the  starlit  depths  of  heaven. 
ISTay,  it  is  even  probable  that  every  flicker  and  corus- 
cation of  our  auroral  displays  corresponds  with  similar 
manifestations  upon  every  planet  which  travels  round 
the  sun.  It  becomes,  then,  a  question  of  exceeding 
interest  to  inquire  what  is  the  nature  of  the  mysterious 
apparition  which  from  tirne'to  time  illuminates  our 
skies.  We  have  learned  something  of  the  laws  accord- 
ing to  which  the  aurora  appears ;  but  what  is  its  true 
nature  ?  What  sort  of  light  is  that  which  illuminates 
the  heavens  ?  Is  there  some  process  of  combustion 
going  on  in  the  upper  regions  of  our  atmosphere  ?  Or 
are  the  auroral  streamers  electric  or  phosphorescent  ? 
Or,  lastly,  is  the  light  simply  solar  light  reflected  from 
some  substance  which  exists  at  an  enormous  elevation 
above  the  earth  ? 


THE  AURORA.  15 

All  these  views  have  from  time  to  time  found  sup- 
porters among  scientific  men.  It  need  hardly  be  said 
that  what  we  now  know  of  the  association  between 
auroral  action  and  some  form  of  solar  disturbance, 
would  at  once  enable  us  to  reject  some  of  these  hy- 
potheses. But  we  need  not  discuss  the  subject  from 
this  point  of  view ;  because  a  mode  of  research  has 
recently  been  rendered  available  which  at  once  an- 
swers our  inquiries  as  to  the  general  character  of  any 
kind  of  light.  I  proceed  to  consider  the  application 
of  this  method  to  the  light  from  the  auroral  streamers. 

The  spectroscope,  or,  as  we  may  term  the  instru- 
ment, the  "light-sifter,"  tells  us  of  what  nature  an 
object  which  is  a  source  of  light  may  be.  If  the  object 
is  a  luminous  solid  or  liquid,  the  instrument  converts 
its  light  into  a  rainbow-colored  streak.  If  the  object 
is  a  luminous  vapor,  its  light  is  converted  into  a  few 
bright  lines.  And,  lastly,  if  the  object  is  a  luminous 
solid  or  liquid  shining  through  any  vapors,  the  rain- 
bow-colored streak  again  makes  its  appearance,  but  it 
is  now  crossed  by  dark  lines,  corresponding  to  the 
vapors  which  surround  the  object  and  absorb  a  portion 
of  its  light. 

But  I  must  not  omit  to  notice  two  circumstances 
which  render  the  interpretation  of  a  spectrum  some- 
what less  simple  than  it  would  otherwise  be. 

In  the  first  place,  if  an  object  is  shining  by  reflected 
light,  its  spectrum  is  precisely  similar  to  that  of  the 


16  LIGHT   SCIENCE  FOR  LEISURE  HOURS. 

object  whose  light  illuminates  it.  Tims  we  cannot 
pronounce  positively  as  to  the  nature  of  an  object 
merely  from  the  appearance  of  its  spectrum,  unless  we 
are  quite  certain  that  the  object  is  self-luminous.  For 
example,  we  observe  the  solar  spectrum  to  be  a  rain- 
bow-colored streak  crossed  by  a  multitude  of  dark  lines, 
and  we  conclude  accordingly  that  the  sun  is  an  incan- 
descent globe  shining  through  a  complex  vaporous  at- 
mosphere. We  feel  no  doubt  on  this  point,  because 
we  are  absolutely  certain  that  the  sun  is  self-luminous. 
Again,  we  observe  the  spectrum  of  the  moon  to  be 
exactly  similar  to  the  solar  spectrum,  only,  of  course, 
much  less  brilliant.  And  here  also  we  feel  no  doubt 
in  interpreting  the  result.  We  know,  certainly,  that 
the  moon  is  not  self-luminous,  and  therefore  we  con- 
clude with  the  utmost  certainty  that  the  light  we  re- 
ceive from  her  is  simply  reflected  solar  light.  So  far 
all  is  clear.  But  now  take  the  case  of  an  object  like 
a  comet,  which  may  or  may  not  be  self-luminous.  If 
we  find  that  a  comet's  spectrum  resembles  the  sun's — 
and  this  is  not  altogether  an  hypothetical  case,  for  a 
portion  of  the  light  of  every  comet  yet  examined  does 
in  reality  give  a  rainbow-colored  streak  resembling  the 
solar  spectrum — we  cannot  form,  in  that  case,  any  such 
positive  conclusion.  The  comet  may  be  a  self-luminous 
body,  but,  on  the  other  hand,  its  light  may  be  due 
merely  to  the  reflection  of  the  solar  beams.  Accord- 
ingly, we  find  that  our  spectroscopists  always  accom- 


THE  AURORA.  17 

pany  the  record  of  such  an  observation  with  an  expres- 
sion of  doubt  as  to  the  real  nature  of  the  object  which 
is  the  source  of  light. 

Secondly,  when  an  electric  spark  flashes  through 
any  vapor,  its  light  gives  a  spectrum  which  indicates 
the  nature,  not  only  of  the  vapor  through  which  the 
spark  has  passed,  but  of  the  substances  between  which 
the  spark  has  travelled.  Thus,  if  we  cause  an  electric 
flash  to  pass  between  iron  points  through  common  air, 
we  see  in  the  spectrum  the  numerous  bright  lines  which 
form  the  spectrum  of  iron,  and  in  addition  we  see  the 
bright  lines  belonging  to  the  gases  which  form  our  at- 
mosphere. 

Both  the  considerations  above  discussed  are  of  the 
utmost  importance  in  studying  the  subject  of  the  au- 
roral light  as  analyzed  by  the  spectroscope,  because 
there  are  many  difficulties  in  forming  a  general  opinion 
as  to  the  nature  of  the  auroral  light,  while  there  are 
circumstances  which  would  lead  us  to  anticipate  that 
the  light  is  electric. 

We  notice  also  in  passing  that  we  owe  to  the  Ger- 
man physicist  Angstrom  a  large  share  of  the  researches 
on  which  the  above  results  respecting  the  spectrum  of 
the  electric  spark  are  founded.  The  reader  will  pres- 
ently see  why  we  have  brought  Angstrom's  name  prom- 
inently forward  in  connection  with  the  interesting 
branch  of  spectroscopic  analysis  just  referred  to.  If 
the  discovery  we  are  approaching  had  been  effected  by 


18  LIGUT  SCIENCE  FOR  LEISURE  HOURS. 

a  tyro  in  the  use  of  the  spectroscope,  doubts  might  very 
reasonably  have  been  entertained  respecting  the  ex- 
actness of  the  observations  on  which  the  discovery 
rests. 

It  was  suggested  many  years  ago,  long  indeed  be- 
fore the  true  powers  of  spectroscopic  analysis  had  been 
revealed,  that  perhaps  if  the  light  of  the  aurora  were 
analyzed  by  the  prism,  evidence  could  be  obtained  of 
its  electric  nature.  The  eminent  meteorologist  Dove 
remarked,  for  instance,  that  "  the  peculiarities  pre- 
sented by  the  electric  light  are  so  marked  that  it  ap- 
pears easy  to  decide  definitely  by  prismatic  analysis, 
whether  the  light  of  the  aurora  is  or  is  not  electric." 
Singularly  enough,  however,  the  first  proof  that  the 
auroral  light  is  of  an  electric  nature  was  derived  from 
a  very  different  mode  of  inquiry.  Dr.  Robinson,  of 
Armagh,  discovered  in  1858  (a  year  before  KirchhofFs 
recognition  of  the  powers  of  spectroscopic  analysis) 
that  the  light  of  the  aurora  possesses  in  a  peculiar  de- 
gree a  property  termed  fluorescence,  which  is  a  recog- 
nized and  characteristic  property  of  the  light  produced 
by  electrical  discharges.  "  These  effects,"  he  remarks 
of  the  appearances  presented  by  the  auroral  light  under 
the  tests  he  applied,  "  were  so  strong  in  relation  to  the 
actual  intensity  of  the  light,  that  they  appear  to  afford 
an  additional  evidence  of  the  electric  origin  of  the  phe- 
nomenon." 

Passing  over  this  ingenious  application  of  one  of 


THE  AURORA.  ]<j 

the  most  singular  and  interesting  properties  of  light, 
we  find  that  the  earliest  determination  of  the  real  na- 
ture of  the  auroral  light — or  rather  of  its  spectrum — 
was  that  effected  by  Angstrom.  This  observer  took 
advantage  of  the  occurrence  of  a  brilliant  aurora  in  the 
winter  of  1867-'68  to  analyze  the  spectrum  of  the  col- 
ored streamers.  A  single  'bright  line  only  was  seen  ! 
Otto  Struve,  an  eminent  Russian  astronomer,  shortly 
afterward  made  confirmatory  observations.  At  the 
meeting  of  the  Royal  Astronomical  Society  in  June, 
1868,  Mr.  Huggins,  F.  R.  S.,  thus  described  Struve's 
results  :  "  In  a  letter,  M.  Otto  Struve  has  informed  me 
that  he  has  had  two  good  opportunities  of  observing 
the  spectrum  of  the  aurora  borealis.  The  spectrum 
consists  of  one  line,  and  the  light  is  therefore  mono- 
chromatic. The  line  falls  near  the  margin  of  the  yel- 
low and  green  portions  of  the  spectrum.  .  .  .  This 
shows  that  the  monochromatic  light  is  greenish,  which 
surprised  me  ;  but  General  Sabine  tells  me  that  in  his 
polar  expeditions  he  has  frequently  seen  the  aurora 
tinged  with  green,  and  this  appearance  corresponds 
with  the  position  of  the  line  seen  by  M.  Struve." 

The  general  import  of  this  observation  there  is  no 
mistaking.  It  teaches  us  that  the  light  of  the  aurora 
is  due  to  luminous  vapor,  and  we  may  conclude,  with 
every  appearance  of  probability,  that  the  luminosity  of 
the  vapor  is  due  to  the  passage  of  electric  discharges 
through  it.  It  is,  however,  possible  that  the  position 


20  LIGHT   SCIENCE  FOR  LEISURE  HOURS. 

of  the  bright  line  may  be  due  to  the  character  of  the 
particles  between  which  the  discharge  takes  place. 

But  the  view  we  are  to  take  must  depend  upon  the 
position  of  the  line.  Here  a  difficulty  presents  itself. 
There  is  no  known  terrestrial  element  whose  spectrum 
has  a  bright  line  precisely  in  the  position  of  the  line  in 
the  auroral  spectrum.  And  mere  proximity  has  no 
significance  whatever  in  spectroscopic  analysis.  Two 
elements  differing  as  much  from  each  other  in  charac- 
ter as  iron  and  hydrogen  may  have  lines  so  closely 
approximating  in  position  that  only  the  most  powerful 
spectroscope  can  indicate  the  difference.  So  that 
when  Angstrom  remarks  that  the  bright  line  he  has 
seen  lies  slightly  to  the  left  of  a  well-known  group  of 
lines  belonging  to  the  metal  calcium  (the  principal 
ingredient  of  common  chalk),  we  are  by  no  means  to 
infer  that  he  supposes  the  substance  which  causes  the 
presence  of  the  bright  line  has  any  resemblance  to  that 
element.  Until  we  can  find  an  element  which  has  a 
bright  line  in  its  spectrum  absolutely  coincident  with 
the  bright  line  detected  by  Angstrom  in  the  spectrum 
of  the  aurora,*  all  speculation  as  to  the  real  nature  of 
the  vapor  in  which  the  auroral  electric  discharge  takes 
place,  or  of  the  substance  between  which  the  spark 
travels,  is  altogether  precluded. 

But  interesting  as  the  discovery  undoubtedly  is, 

*  Other  green  lines  have  since  been  discovered  in  the  auroral  spec- 
trum ;  and  occasionally  a  red  line  is  seen. 


THE  AURORA.  21 

we  have  now  to  deal  with  one  of  a  yet  more  interest- 
ing character. 

Most  of  my  readers  have  doubtless  heard  of  the 
zodiacal  light,  and  many  of  them  have  perhaps  seen 
that  mysterious  radiance,  pointing  obliquely  upward 
from  the  western  horizon  soon  after  sunset  in  the 
spring  months,  or  in  autumn  shortly  before  sunrise, 
above  the  eastern  horizon.  The  light,  as  its  name 
indeed  implies,  lies  upon  that  region  of  the  heavens 
along  which  the  planets  travel.  Accordingly,  astron- 
omers have  associated  it  with  the  planetary  orbits,  and 
have  come  to  look  on  it  as  formed  by  the  light  reflected 
from  a  multitude  of  minute  bodies  travelling  around 
the  sun  within  the  orbit  of  our  earth. 

Yet  it  had  long  been  recognized  that  there  are 
difficulties  in  the  way  of  this  theory.  Passing  over 
those  which  depend  On  the  position  of  the  zodiacal 
light  upon  the  heavens,  there  are  difficulties  connected 
with  the  appearance  of  the  object.  For  example,  its 
light  has  often  been  observed  to  flicker  or  coruscate  in 
a  manner  which  it  seemed  difficult  to  ascribe  to  the 
motions  of  our  own  atmosphere.  Then  again  there 
have  been  seasons  when  the  zodiacal  light  has  shone 
with  unusual  intensity  for  months  together,  and  there 
is  nothing  in  the  received  theory  which  can  account 
for  such  a  peculiarity.  Lastly,  there  is  the  strange 
circumstance  recorded  by  Baron  Humboldt  that  the 
zodiacal  light  is  often  invisible  when  night  first  sets  in, 


22  LIGHT   SCIENCE  FOR  LEISURE  HOURS. 

and  then  suddenly  appears  with,  full  splendor;  a  phe- 
nomenon which  is  utterly  inexplicable  if  the  received 
theory  be  accepted.  The  whole  account  of  the  phe- 
nomenon, as  given  by  Baron  Humboldt,  is  so  interest- 
ing, and  for  my  present  purpose  so  significant,  that  I 
give  it  at  full  length  : 

"In  the  tropical  climate  of  South  America,"  he 
remarks,  "  the  variable  strength  of  the  light  of  the 
zodiacal  gleam  struck  me  at  times  with  utter  amaze- 
ment. As  I  there  passed  the  beautiful  nights^  in  the 
open  air,  on  the  banks  of  rivers,  and  in  the  grassy 
plains  for  several  months  together,  I  had  opportunities 
of  observing  the  phenomenon  with  attention.  "When 
the  zodiacal  light  was  at  its  very  brightest,  it  some- 
times happened  that  but  a  few  mintues  afterward  it 
became  notably  weakened,  and  then  it  suddenly 
gleamed  up  again  with  its  former  brilliancy.  In  par- 
ticular instances,  I  believed  that  I  remarked — not  any 
tiling  of  a  ruddy  tinge,  or  an  interior  arched  obscura- 
tion, or  an  emission  of  sparks,  such  as  Mairan  describes, 
but — a  kind  of  unsteadiness  and  flickering  of  the 
light." 

Despite  these  and  similar  observations,  very  little 
doubt  had  been  felt  by  astronomers  that  the  zodiacal 
light  really  indicates  the  presence  of  minute  bodies 
travelling  in  more  or  less  eccentric  paths  round  the 
sun.  And  it  was  confidently  expected  that  whenever 
a  spectroscope  of  sufficient  delicacy  to  analyze  the  faint 


THE  AURORA.  23 

light  of  the  zodiacal  gleam  was  applied  to  that  pur- 
pose, the  resulting  spectrum  would  be  merely  a  very 
faint  reproduction  of  the  solar  spectrum. 

Recently,  however,  the  zodiacal  light  has  been  ana- 
lyzed by  Angstrom,  with  a  result  altogether  unexpected, 
and  at  present  almost  unintelligible.  Its  spectrum 
exhibits  a  "bright  line,  and  this  bright  line  is  the  same 
that  is  seen  in  the  spectrum  of  the  aurora  'borealis  ! 

How  are  we  to  understand  this  most  surprising 
result  ?  Remembering  that  the  aurora  is  undoubtedly 
a  terrestrial  light,  whencesoever  it  derives  its  lumi- 
nosity— in  other  words,  that  the  electric  discharges, 
however  excited,  really  take  place  in  the  upper  regions 
of  our  own  atmosphere,  while  as  certainly  the  zodiacal 
light  is  an  extra-terrestrial  phenomenon — the  observed 
phenomenon  becomes  one  of  the  most  perplexing  dis- 
coveries ever  made  by  man.  That  it  will  before  long 
be  interpreted  we  have  no  doubt  whatever ;  nor  do  we 
doubt  that  the  interpretation  will  involve  the  explana- 
tion of  a  whole  series  of  phenomena  which  have  lately 
perplexed  astronomers.  Recalling  the  association  be- 
tween auroras  and  terrestrial  magnetism,  and  that 
between  terrestrial  magnetism  and  the  solar  spots,  and 
remembering  further  that  our  physicists  have  recently 
detected  well-marked  signs  that  the  planets  in  their 
courses  influence  the  sun's  atmosphere  and  generate 
his  spots  in  some  manner  as  yet  unexplained,  we  see 
that  the  one  fact  wanting  to  explain  Angstrom's  dis- 


24  LIGHT   SCIENCE  FOR  LEISURE  HOURS. 

covery  is  undoubtedly  not  an  isolated  fact,  but  must  be 
associated  in  the  most  intimate  manner  with  a  variety 
of  important  cosmical  relations.  To  speculate  as  to 
the  nature  of  the  as  yet  undiscovered  interpretation 
of  Angstrom's  researches  would  at  present  be  an  idle 
task,  perhaps.  But  one  feature  of  the  solar  scheme 
with  which  we  cannot  doubt  that  it  will  be  found  to 
be  associated,  must  be  mentioned  before  we  conclude. 

Of  all  the  phenomena  presented  to  the  contempla- 
tion of  astronomers,  the  tails  of  comets  are  undoubted- 
ly the  most  perplexing.  Their  rapid  formation,  their 
swift  motions  (if,  indeed,  we  could  believe  that  their 
changes  of  position  are  due  to  a  real  transmission  of 
their  material  substance),  and  the  enormous  variety  of 
configuration  and  of  structure  which  they  present  to 
our  contemplation,  render  them  not  merely  amazing, 
but  altogether  unintelligible. 

!Nbw,  there  is  one  feature  of  comets'  tails  which  has 
long  since  attracted  attention,  and  will  remind  the 
reader  of  the  peculiarities  common  to  the  zodiacal  and 
the  auroral  light.  "We  refer  to  the  sudden  changes 
of  brilliancy,  the  flickerings  or  coruscations,  and  the 
instantaneous  lengthening  and  shortening  of  these 
mysterious  appendages.  Olbers  spoke  of  "  explosions 
and  pulsations  which  in  a  few  seconds  went  trembling 
through  the  whole  length  of  a  comet's  tail,  with  the 
effect  now  of  lengthening,  now  of  abridging  it  by 
several  degrees."  And  the  eminent  mathematician 


THE   AURORA.  25 

Euler  was  led  by  tlie  observation  of  similar  appearances 
to  put  forward  the  theory  "  that  there  is  a  great  affinity 
between  these  tails,  the  zodiacal  light,  and  the  aurora 
borealis"  The  late  Admiral  Smyth,  commenting  on 
this  opinion  of  Euler's,  remarks  that  "most  reasoners 
seem  now  to  consider  comets'  tails  as  consisting  of 
electric  matter ;  "  adding  that  "  this  would  account  for 
the  undulations  and  other  appearances  which  have 
been  noticed,  as,  for  instance,  that  extraordinary  one 
seen  by  M.  Chladni  in  the  comet  of  1811,  when  certain 
undulatory  ebullitions  rushed  from  the  nucleus  to  the 
end  of  the  tail,  a  distance  of  more  than  ten  millions 
of  miles,  in  two  or  three  seconds  of  time."  To  this 
we  may  add  the  somewhat  bizarre  theory  suggested  by 
Sir  John  Herschel,  that  the  matter  forming  the  zodia- 
cal light  is  "  loaded,  perhaps,  with  the  actual  materials 
of  the  tails  of  millions  of  comets,  which  have  been 
stripped  of  these  appendages  in  the  course  of  successive 
passages  round  the  immediate  neighborhood  of  the  sun." 
Now,  hitherto  no  comet  with  a  sufficiently  brilliant 
tail  for  spectroscopic  analysis  has  appeared  since  Kirch- 
hoff 's  invention  of  that  mode  of  research.  Already 
our  physicists  had  been  looking  forward  anxiously  for 
the  appearance  of  such  a  comet  as  Donati's  or  Halley's. 
But  Angstrom's  recent  discovery,  and  the  evidence 
which  seems  to  associate  the  tails  of  comets  with  the 
auroral  and  zodiacal  lights,  render  our  spectroscopists 
doubly  anxious  to  submit  a  comet's  tail  to  spectroscopic 


26  LIGHT   SCIENCE  FOR  LEISURE  HOURS. 

analysis.  It  is  far  from  being  unlikely  that  three 
long-vexed  questions — the  nature  of  the  aurora,  and 
that  of  the  zodiacal  light,  and  that  of  comets'  tails — 
will  receive  their  solution  simultaneously. 

I  had  scarcely  completed  the  above  pages  when 
news  was  brought  from  America  that  the  spectrum  of 
the  sun's  corona,  as  seen  during  the  recent  total  solar 
eclipse,  exhibited  the  same  bright  lines  as  the  aurora. 
The  fact  that  auroral  lines  are  mentioned  will  at  once 
l)e  noticed ;  but  it  is  to  be  remarked  that  the  two  faint 
lines  which  have  been  lately  seen  in  the  auroral  spec- 
trum correspond  to  but  a  very  small  portion  of  the 
light  we  receive  from  the  northern  streamers.  In  the 
spectrum  of  the  corona  the  same  three  lines  appear, 
but  their  relative  brightness  is  different.  The  bright- 
est line  of  the  auroral  spectrum  is  faint  in  the  spectrum 
of  the  corona,  while  the  latter  exhibits  a  bright  line 
where  the  former  has  a  faint  one. 

News  has  also  been  received  that  a  comparison  of 
the  photographs  of  the  eclipse  proves  the  corona,  or  at 
any  rate  its  brightest  part,  to  belong  to  the  sun. 

Lastly,  it  has  been  found  that  the  peculiar  phospho- 
rescent light  sometimes  visible  all  over  the  sky  at  night 
gives  the  same  spectrum  (very  faint,  of  course)  as  the 
aurora  and  the  zodiacal  light. 

It  is  impossible  not  to  recognize  the  fact  that  these 
discoveries  point  to  relations  of  the  utmost  importance. 
The  teachings  of  the  spectroscope  are  too  certain  to  be 


THE  AURORA.  27 

mistaken.  "When  it  shows  us  such  and  such  lines 
bright  or  dark,  we  may  conclude,  without  fear  of  being 
misled,  that  such  and  such  substances  are  emitting  or 
absorbing  light.  "What  we  learn  certainly,  therefore, 
from  the  facts  above  stated,  is  this,  that  substances  of 
the  same  sort  emit  the  light  of  the  aurora,  of  the  zodia- 
cal gleam,  of  the  sun's  corona,  and  of  the  phosphores- 
cence which  illuminates  at  times  the  nocturnal  skies. 
We  may  conclude,  but  not  so  certainly,  that  the  manner 
in  which  the  light  is  emitted  is  also  the  same  in  each  case. 
We  know  certainly  that  the  auroral  light  is  excited  by 
the  solar  action.  We  know  certainly  that  it  is  associ- 
ated with  the  earth's  magnetism.  The  opinion,  then, 
which  we  should  form  of  the  source  to  which  the  other 
lights  are  due  is  tolerably  obvious.  So  long  as  elec- 
tricity was  merely  used  as  a  convenient  way  of  account- 
ing for  any  perplexing  phenomenon,  it  was  impossible 
to  accept  explanations  of  cosmical  peculiarities  as  due 
to  electrical  action.  But  when  once  we  have  reason 
— as  in  the  case  of  the  aurora  we  undoubtedly  have — to 
associate  electricity  with  any  particular  form  of  lumi- 
nosity, we  seem  clearly  justified  in  extending  the  ex- 
planation to  the  same  form  of  luminosity  wherever 
it  may  appear. 

I  believe  that  the  key  to  the  whole  series  of  phe- 
nomena dealt  with  above  lies  in  the  existence  of  myriads 
of  meteoric  bodies  travelling  separately  or  in  systems 
round  the  sun.  They  are  consumed  in  thousands 


28  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

daily  by  our  own  atmosphere ;  they  probably  pour  in 
countless  millions  upon  the  solar  atmosphere ;  and  from 
what  we  know  of  their  numbers  in  our  own  neighbor- 
hood, and  of  the  probability  of  their  being  infinitely 
more  numerous  in  the  neighborhood  of  the  sun,  we 
have  excellent  reasons  for  believing  that  to  them  prin- 
cipally is  due  the  appearance  of  the  zodiacal  light  and 
the  solar  corona. 

(From  Frascr^e  Magazine,  February,  1870.) 


THE  EARTH  A  MAGNET. 

THERE  is  a  very  prevalent  but  erroneous  opinion 
that  the  magnetic  needle  points  to  the  north.  "We 
remember  well  how  we  discovered  in  our  boyhood  that 
the  needle  does  not  point  to  the  north,  for  the  discovery 
was  impressed  upon  us  in  a  very  unpleasant  manner. 
"We  had  purchased  a  pocket-compass,  and  were  very 
anxious — not,  indeed,  to  test  the  instrument,  since  we 
placed  implicit  reliance  upon  its  indications — but  to 
make  use  of  it  as  a  guide  across  unknown  regions. 
Not  many  miles  from  where  we  lived  lay  Cobham 
"Wood,  no  very  extensive  forest  certainly,  but  large 
enough  to  lose  one's  self  in.  Thither,  accordingly,  we 
proceeded  with  three  school-fellows.  "When  we  had 
lost  ourselves,  we  gleefully  called  the  compass  into 
action,  and  made  from  the  wood  in  a  direction  which 


THE  EARTH  A  MAGNET.  29 

we  supposed  would  lead  us  home.  We  travelled  on 
with  full  confidence  in  our  pocket-guide ;  at  each  turn- 
ing we  consulted  it  in  an  artistic  manner,  carefully 
poising  it  and  waiting  till  its  vibrations  ceased.  But 
when  we  had  travelled  some  two  or  three  miles  without 
seeing  any  house  or  road  that  we  recognized,  matters 
assumed  a  less  cheerful  aspect.  "We  were  unwilling  to 
compromise  our  dignity  as  "  explorers  "  by  asking  the 
way — a  proceeding  which  no  precedent  in  the  history 
of  our  favorite  travellers  allowed  us  to  think  of.  But 
evening  came  on,  and  with  it  a  summer  thunder- 
storm. We  were  getting  thoroughly  tired  out,  and  the 
hcBG  olim  meminisse  juvdbit  with  which  we  had  been 
comforting  ourselves  began  to  lose  its  force.  "When 
at  length  we  yielded,  we  learned  that  we  had  gone 
many  miles  out  of  our  road,  and  we  did  not  reach 
home  till  several  hours  after  dark.  How  it  fared  with 
our  school-fellows  we  know  not,  but  a  result  overtook 
ourselves  personally,  for  which  there  is  no  precedent, 
so  far  as  we  are  aware,  in  the  records  of  exploring 
expeditions.  Also  the  offending  compass  was  con- 
fiscated by  justly  indignant  parents,  so  that  for  a  long 
while  the  cause  of  our  troubles  was  a  mystery  to  us. 
We  now  know  that  instead  of  pointing  due  north,  the 
compass  pointed  more  than  20°  toward  the  west,  or 
nearly  to  the  quarter  called  by  sailors  north-northwest. 
No  wonder,  therefore,  that  we  went  astray  when  we 
followed  a  guide  so  untrustworthy. 


30  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

The  peculiarity  that  the  magnet  needle  does  not, 
in  general,  point  to  the  north,  is  the  first  of  a  series  of 
peculiarities  which  we  now  propose  briefly  to  describe. 
The  irregularity  is  called  by  sailors  the  needle's  varia- 
tion, but  the  term  more  commonly  used  by  scientific 
men  is  the  declination  of  the  needle.  It  was  probably 
discovered  a  long  time  ago,  for  800  years  before  our 
era  the  Chinese  applied  the  magnet's  directive  force  to 
guide  them  in  journeying  over  the  great  Asiatic  plains ; 
and  they  must  soon  have  detected  so  marked  a  peculi- 
arity. Instead  of  a  ship's  compass,  they  made  use  of 
a  magnetic  car,  on  the  front  of  which  a  floating  needle 
carried  a^mall  figure,  whose  outstretched  arm  pointed 
southward.  "We  have  no  record,  however,  of  their 
discovery  of  the  declination,  and  know  only  that  they 
were  acquainted  with  it  in  the  twelfth  century.  The 
declination  was  discovered,  independently,  by  European 
observers  in  the  thirteenth  century. 

As  we  travel  from  place  to  place,  the  declination  of 
the  needle  is  found  to  vary.  Christopher  Columbus 
was  the  first  to  detect  this.  He  discovered  it  on  the 
13th  of  September,  1492,  during  his  first  voyage,  and 
when  he  was  six  hundred  miles  from  Ferro,  the  most 
westerly  of  the  Canary  Islands.  He  found  that  the 
declination,  which  was  toward  the  east  in  Europe, 
passed  to  the  west,  and  increased  continually  as  he 
travelled  westward. 

But  here  we  see  the  first  trace  of  a  yet  more  singu- 


THE   EARTH  A   MAGNET.  31 

*ar  peculiarity.  We  have  said  that  at  present  the  dec- 
lination is  toward  the  west  in  Europe.  In  Columbus's 
time  it  was  toward  the  east.  Thus  we  learn  that  the 
declination  varies  with  the  progress  of  time,  as  well  as 
with  change  of  place. 

The  genius  of  modern  science  is  a  weighing  and  a 
measuring  one.  Men  are  not  satisfied  nowadays  with 
knowing  that  a  peculiarity  exists  ;  they  seek  to  deter- 
mine its  extent,  how  far  it  is  variable — whether  from 
time  to  time  or  from  place  to  place,  and  so  on.  Now 
the  results  of  such  inquiries  applied  to  the  magnetic 
declination  have  proved  exceedingly  interesting. 

"We  find,  first,  that  the  world  may  be  divided  into 
two  unequal  portions,  over  one  of  which  the  needle  has 
a  westerly,  and  over  the  other  an  easterly,  declination. 
Along  the  boundary-line,  of  course,  the  needle  points 
due  north.  England  is  situated  in  the  region  of  west- 
erly magnets.  This  region  includes  all  Europe,  except 
the  northeastern  parts  of  Russia  ;  Turkey,  Arabia,  and 
the  whole  of  Africa ;  the  greater  part  of  the  Indian 
Ocean,  and  the  western  parts  of  Australia  ;  nearly  the 
whole  of  the  Atlantic  Ocean  ;  Greenland,  the  eastern 
parts  of  Canada,  and  a  small  slice  from  the  northeastern 
part  of  Brazil.  All  these  form  one  region  of  westerly 
declination  ;  but,  singularly  enough,  there  lies  in  the 
very  heart  of  the  remaining  and  larger  region  of  east- 
erly magnets  an  oval  space  of  a  contrary  character. 
This  space  includes  the  Japanese  Islands,  Mantchooria, 


32  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

and  the  eastern  parts  of  China.  It  is  very  noteworthy 
also,  that  in  the  westerly  region  the  declination  is  much 
greater  than  in  the  easterly.  Over  the  whole  of  Asia, 
for  instance,  the  needle  points  almost  due  north.  On 
the  contrary,  in  the  north  of  Greenland  and  of  Baffin's 
Bay,  the  magnetic  needle  points  due  west ;  while  still 
farther  to  the  north  (a  little  westerly),  we  find  the 
needle  pointing  with  its  north  end  directly  toward  the 
south. 

In  the  presence  of  these  peculiarities,  it  would  be 
pleasant  to  speculate.  We  might  imagine  the  existence 
of  powerfully  magnetic  veins  in  the  earth's  solid  mass, 
coercing  the  magnetic  needle  from  a  full  obedience  to 
the  true  polar  summons.  Or  the  comparative  effects 
of  oceans  and  of  continents  might  be  called  into  play. 
But,  unfortunately  for  all  this,  we  have  to  reconcile 
views  founded  on  fixed  relations  presented  by  the  earth 
with  the  process  of  change  indicated  above.  Let  us 
consider  the  declination  in  England  alone. 

In  the  fifteenth  century  there  was  an  easterly  dec- 
lination. This  gradually  diminished,  so  that  in  about 
the  year  1657  the  needle  pointed  due  north.  After 
this  the  needle  pointed  toward  the  west,  and  contin- 
ually more  and  more,  so  that  scientific  men,  having 
had  experience  only  of  a  continual  shifting  of  the 
needle  in  one  direction,  began  to  form  the  opinion  that 
this  change  would  continue,  so  that  the  needle  would 
pass,  through  northwest  and  west,  to  the  south.  In 


THE  EARTH  A  MAGNET.  33 

fact,  it  was  imagined  that  the  motion  of  the  needle 
would  resemble  that  of  the  hands  of  a  watch,  only  in  a 
reversed  direction.  But  before  long  observant  men 
detected  a  gradual  diminution  in  the  needle's  westerly 
motion.  Arago,  the  distinguished  French  astronomer 
and  physicist,  was  the  first  (we  believe)  to  point  out 
that  "  the  progressive  movement  of  the  magnetic  needle 
toward  the  west  appeared  to  have  become  continually 
slower  of  late  years "  (he  wrote  in  1814),  "  which 
seemed  to  indicate  that  after  some  little  time  longer  it 
might  become  retrograde."  Three  years  later,  namely, 
on  the  10th  of  February,  1817,  Arago  asserted  defini- 
tively that  the  retrograde  movement  of  the  magnetic 
needle  had  commenced  to  be  perceptible.  Colonel 
Beaufoy  at  first  oppugned  Arago's  conclusion,  for  he 
found  from  observations  made  in  London  during  the 
years  1817-1819,  that  the  westerly  motion  still  con- 
tinued. But  he  had  omitted  to  take  notice  of  one  very 
simple  fact,  viz.,  that  London  and  Paris  are  two  differ- 
ent places.  A  few  years  later  the  retrograde  motion 
became  perceptible  at  London  also,  and  it  has  now  been 
established  by  the  observations  of  forty  years.  It  ap- 
pears, from  a  careful  comparison  of  Beaufoy's  observa- 
tions, that  the  needle  reached  the  limit  of  its  western 
digression  (at  Greenwich)  in  March,  1819,  at  which 
time  the  declination  was  very  nearly  25°.  In  Paris, 
on  the  contrary,  the  needle  had  reached  its  greatest 
western  digression  (about  22-£°)  in  1814,  It  is  rather 


34  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

singular  that,  althongli  at  Paris  the  retrograde  motion 
thus  presented  itself  five  years  earlier  than  in  London, 
the  needle  pointed  due  north  at  Paris  six  years  later 
than  in  London,  viz.,  in  1663.  Perhaps  the  greater 
amplitude  of  the  needle's  London  digression  may  ex- 
plain this  peculiarity. 

"  It  was  already  sufficiently  difficult,"  says  Arago, 
"  to  imagine  what  could  be  the  kind  of  change  in  the 
constitution  of  the  globe  which  could  act  during  one 
hundred  and  fifty-three  years  in  gradually  transferring 
the  direction  of  the  magnetic  needle  from  due  north  to 
23°  west  of  north.  We  see  that  it  is  now  necessary  to 
explain,  moreover,  how  it  has  happened  that  this  grad- 
ual change  has  ceased,  and  has  given  place  to  a  return 
toward  the  preceding  state  of  the  globe."  "  How  is 
it,"  he  pertinently  asks,  "  that  the  directive  action  of 
the  globe,  which  clearly  must  result  from  the  action 
of  molecules  of  which  the  globe  is  composed,  can  be 
thus  variable,  while  the  number,  position,  and  tempera- 
ture of  these  molecules,  and,  as  far  as  we  know,  all 
their  other  physical  properties,  remain  constant  ? " 

But  we  have  considered  only  a  single  region  of  the 
earth's  surface.  Arago's  opinion  will  seem  still  more 
just  when  we  examine  the  change  which  has  taken 
place  in  what  we  may  terrn  the  "  magnetic  aspect "  of 
the  whole  globe.  The  line  which  separates  the  region 
of  westerly  magnets  from  the  region  of  easterly 
magnets  now  runs,  as  we  have  said,  across  Canada  and 


THE  EARTH  A   MAGNET.  35 

eastern  Brazil  in  one  hemisphere,  and  across  Russia, 
Asiatic  Turkey,  the  Indian  Ocean,  and  West  Australia, 
in  the  other ;  besides  having  an  outlying  oval  to  the 
east  of  the  Asiatic  continent.  ~Now  these  lines  have 
swept  round  a  part  of  the  globe's  circuit  in  a  most 
singular  manner  since  1600.  They  have  varied  alike 
in  direction  and  complexity.  The  Siberian  oval,  now 
distinct,  was  in  1787  merely  a  loop  of  the  eastern  line 
of  no  declination.  The  oval  appears  now  to  be  con- 
tinually diminishing,  and  will  one  day  probably  dis- 
appear. 

We  find  here  presented  to  us  a  phenomenon  as 
mysterious,  as  astonishing,  and  as  worthy  of  careful 
study,  as  any  embraced  in  the  wide  domains  of  science. 
But  other  peculiarities  await  our  notice. 

If  a  magnetic  needle  of  suitable  length  be  carefully 
poised  on  a  fine  point,  or,  better,  be  suspended  from  a 
silk  thread  without  torsion,  it  will  be  found  to  exhibit 
each  day  two  small,  but  clearly  perceptible,  oscillations. 
M.  Arago,  from  a  careful  series  of  observations,  deduced 
the  following  results : 

At  about  eleven  at  night,  the  north  end  of  the 
needle  begins  to  move  from  west  to  east,  and  having 
reached  its  greatest  easterly  excursion  at  about  a  quar- 
ter-past eight  in  the  morning,  returns  toward  the  west 
to  attain  its  greatest  westerly  excursion  at  a  quarter-past 
one.  It  then  moves  again  to  the  east,  and  having 
reached  its  greatest  easterly  excursion  at  half-past  eight 


36  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

in  the  evening,  returns  to  the  west,  and  attains  its  great- 
est westerly  excursion  at  eleven,  as  at  starting. 

Of  course,  these  excursions  take  place  on  either  side 
of  the  mean  position  of  the  needle,  and  as  the  excursions 
are  small,  never  exceeding  the  fifth  part  of  a  degree, 
while  the  mean  position  of  the  needle  lies  some  20°  to 
the  west  of  north,  it  is  clear  that  the  excursions  are 
only  nominally  eastern  and  western,  the  needle  point- 
ing, throughout,  far  to  the  west. 

iNow  if  we  remember  that  the  north  end  of  the  nee- 
dle is  that  farthest  from  the  sun,  it  will  be  easy  to  trace 
in  M.  Arago's  results  a  sort  of  effort  on  the  part  of  the 
needle  to  turn  toward  the  sun — not  merely  when  that 
luminary  is  above  the  horizon,  but  during  his  noctur- 
nal path  also. 

"We  are  prepared,  therefore,  to  expect  that  a  varia- 
tion, having  an  annual  period,  shall  appear,  on  a  close 
observation  of  our  suspended  needle.  Such  a  varia- 
tion has  been  long  since  recognized.  It  is  found  that  in 
the  summer  of  both  hemispheres,  the  daily  variation  is 
exaggerated,  while  in  winter  it  is  diminished. 

But  besides  the  divergence  of  a  magnetized  needle 
from  the  north  pole,  there  is  a  divergence  from  the 
horizontal  position  which  must  now  claim  our  atten- 
tion. If  a  non-magnetic  needle  be  carefully  suspended 
so  as  to  rest  horizontally,  and  be  then  magnetized,  it 
will  be  found  no  longer  to  preserve  that  position.  The 
northern  end  dips  very  sensibly.  This  happens  in  our 


THE  EARTH  A  MAGNET.  37 

Jiemi sphere.  In  the  southern,  it  is  the  southern  end 
which  dips.  It  is  clear,  therefore,  that  if  we  travel 
from  one  hemisphere  to  the  other,  we  must  find  the 
northern  dip  of  the  needle  gradually  diminishing,  till  at 
some  point  near  the  equator  the  needle  is  horizontal ; 
and  as  we  pass  thence  to  southern  regions,  a  gradually 
increasing  southern  inclination  is  presented.  This  has 
been  found  to  be  the  case,  and  the  position  of  the  line 
along  which  there  is  no  inclination  (called  the  magnetic 
equator)  has  been  traced  around  the  globe.  It  is  not 
coincident  with  the  earth's  equator,  but  crosses  that 
circle  at  an  angle  of  twelve  degrees,  passing  from  north 
to  south  of  the  equator  in  long.  3°  west  of  Greenwich, 
and  from  south  to  north  in  long.  187°  east  of  Green- 
wich. The  form  of  the  line  is  not  exactly  that  of  a 
great  circle,  but  presents  here  and  there  (and  especially 
where  it  crosses  the  Atlantic)  perceptible  excursions 
from  such  a  figure. 

At  two  points  on  tne  earth's  globe  the  needle  will 
rest  in  a  vertical  position.  These  are  the  magnetic 
poles  of  the  earth.  The  northern  magnetic  pole  waa 
reached  by  Sir  J.  G.  Ross,  and  lies  in  70°  JS".  lat.  and 
263°  E.  long.,  that  is,  to  the  north  of  the  American 
Continent,  and  not  very  far  from  Boothia  Gulf.  One 
of  the  objects  with  which  Ross  set  out  on  his  celebrated 
expedition  to  the  Antarctic  Seas  was  the  discovery,  if 
possible,  of  the  southern  magnetic  pole.  In  this  he 
was  not  successful.  Twice  he  was  in  hopes  of  attaining 


38  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

his  object,  but  each  time  he  was  stopped  by  a  barrier 
of  land.  He  approached  so  near,  however,  to  the  pole, 
that  the  needle  was  inclined  at  an  angle  of  nearly 
ninety  degrees  to  the  horizon,  and  he  was  able  to 
assign  to  the  southern  pole  a  position  in  75°  S.  lat., 
154°  E.  long.  It  is  not  probable,  we  should  imagine, 
that  either  pole  is  fixed,  since  we  shall  now  see  that 
the  inclination,  like  the  declination  of  the  magnetic 
needle,  is  variable  from  time  to  time,  as  well  as  from 
place  to  place  ;  and  in  particular,  the  magnetic  equator 
is  apparently  subjected  to  a  slow  but  uniform  Drocess 
of  change. 

Arago  tells  us  that  the  inclination  of  the  needle  at 
Paris  has  been  observed  to  diminish  year  by  year  since 
1671.  At  that  time  the  inclination  was  no  less  than 
75°  ;  in  other  words,  the  needle  was  inclined  only  15° 
to  the  vertical.  In  1791  the  inclination  was  less  than 
71°.  In  1831  it  was  less  than  68°.  In  like  manner, 
the  inclination  at  London  has  been  observed  to  dimin- 
ish, from  72°  in  1786  to  70°  in  1804,  and  thence  to  68° 
at  the  present  time. 

It  might  be  anticipated  from  such  changes  as  these 
that  the  magnetic  equator  would  be  found  to  be 
changing  in  position.  Nay,  we  can  even  guess  in  which 
way  it  must  be  changing.  For,  since  the  inclination  is 
diminishing  at  London  and  Paris,  the  magnetic  equa- 
tor must  be  approaching  these  places,  and  this  (in  the 
present  position  of  the  curve)  can  only  happen  by  a 


THE  EARTH  A  MAGNET.  39 

gradual  shifting  of  the  magnetic  equator  from  east  to 
west  along  the  true  equator.  This  motion  .has  been 
found  to  be  really  taking  place.  It  is  supposed  that 
the  movement  is  accompanied  by  a  change  of  form ; 
but  more  observations  are  necessary  to  establish  this 
interesting  point. 

Can  it  be  doubted  that  while  these  changes  are 
taking  place,  the  magnetic  poles  also  are  slowly  shifting 
round  the  true  pole  ?  Must  not  the  northern  pole,  for 
instance,  be  farther  from  Paris  now  that  the  needle  is 
inclined  more  than  23°  from  the  vertical,  than  in  16Y1, 
when  the  inclination  was  only  15°  ?  It  appears  obvi- 
ous that  this  must  be  so,  and  we  deduce  the  interesting 
conclusion  that  each  of  the  magnetic  poles  is  rotating 
around  the  earth's  axis. 

But  there  is  another  peculiarity  of  the  needle  which 
is  as  noteworthy  as  any  of  those  we  have  spoken  about. 
"We  refer  to  the  intensity  of  the  magnetic  action — the 
energy  with  which  the  needle  seeks  its  position  of 
rest.  This  is  not  only  variable  from  place  to  place, 
but  from  time  to  time,  and  is  further  subject  to  sudden 
changes  of  a  very  singular  character. 

It  might  be  expected  that  where  the  dip  is  greater, 
the  directive  energy  of  the  magnet  would  be  propor- 
tionately great.  And  this  is  found  to  be  approximately 
the  case.  Accordingly,  the  magnetic  equator  is  very 
nearly  coincident  with  the  "  equator  of  least  intensity," 
but  not  exactly.  As  \ve  approach  the  magnetic  poles 


40  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

we  find  a  more  considerable  divergence,  so  that  instead 
of  there  being  a  northern  pole  of  greatest  intensity 
nearly  coincident  with  the  northern  magnetic  pole, 
which  we  have  seen  lies  to  the  north  of  the  American 
Continent,  there  are  two  northern  poles,  one  in  Siberia 
nearly  at  the  point  where  the  river  Lena  crosses  the 
Arctic  circle,  the  other  not  so  far  to  the  north — only  a 
few  degrees  north,  in  fact,  of  Lake  Superior.  In  the 
south,  in  like  manner,  there  are  also  two  poles,  one  on 
the  Antarctic  circle,  abotit  130°  E.  long.,  in  Adelie 
Island,  the  other  not  yet  precisely  determined,  but 
supposed  to  lie  on  about  the  240th  degree  of  longitude, 
and  south  of  the  Antarctic  circle.  Singularly  enough, 
there  is  a  line  of  lower  intensity  running  right  round 
the  earth  along  the  valleys  of  the  two  great  oceans, 
"  passing  through  Behring's  Straits  and  bisecting  the 
Pacific,  on  one  side  of  the  globe,  and  passing  out  of 
the  Arctic  Sea  by  Spitzbergen  and  down  the  Atlantic, 
on  the  other." 

General  Sabine  discovered  that  the  intensity  of  the 
magnetic  action  varies  during  the  course  of  the  year. 
It  is  greatest  in  December  and  January  in  1>oth  hemi- 
spheres. If  the  intensity  had  been  greatest  in  winter, 
one  would  have  been  disposed  to  have  assigned  sea- 
sonal variation  of  temperature  as  the  cause  of  the 
change.  But  as  the  epoch  is  the  same  for  both  hemi- 
spheres, we  must  seek  another  cause.  Is  there  any 
astronomical  element  which  seems  to  correspond  with 


THE  EARTH  A  MAGNET.  41 

the  law  discovered  by  Sabine  ?  There  is  one  very  im- 
portant element.  The  position  of  the  perihelion  of  the 
earth's  orbit  is  such  that  the  earth  is  nearest  to  the  sun 
on  about  the  31st  of  December  or  the  1st  of  January. 
There  seems  nothing  rashly  speculative,  then,  in  con- 
cluding that  the  sun  exercises  a  magnetic  influence  on 
the  earth,  varying  according  to  the  distance  of  the 
earth  from  the  sun.  Nay,  Sabine's  results  seem  to 
point  very  distinctly  to  the  law  of  variation.  For, 
although  the  number  of  observations  is  not  as  yet  very 
great,  and  the  extreme  delicacy  of  the  variation  ren- 
ders the  determination  of  its  amount  very  difficult, 
enough  has  been  done  to  show  that  in  all  probability 
the  sun's  influence  varies  according  to  the  same  law  as 
gravity — that  is,  inversely  as  the  square  of  the  dis- 
tance. 

That  the  sun,  the  source  of  light  and  heat,  and  the 
great  gravitating  centre  of  the  solar  system,  should 
exercise  a  magnetic  influence  upon  the  earth,  and  that 
this  influence  should  vary  according  to  the  same  law 
as  gravity,  or  as  the  distribution  of  light  and  heat,  will 
not  appear  perhaps  very  surprising.  But  the  discovery 
by  Sabine  that  the  moon  exercises  a  distinctly  traceable 
effect  upon  the  magnetic  needle  seems  to  us  a  very 
remarkable  one.  We  receive  very  little  light  from  the 
moon,  much  less  (in  comparison  with  the  sun's  light) 
than  most  persons  would  suppose,  and  we  get  abso- 
lutely no  perceptible  heat  from  her.  Therefore  it 


42  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

would  seem  rather  to  the  influence  of  mass  and  prox- 
imity that  the  magnetic  disturbances  caused  by  the 
moon  must  be  ascribed.  But  if  the  moon  exercises  an 
influence  in  this  way,  why  should  not  the  planets? 
"We  shall  see  that  there  is  evidence  of  some  such  in- 
fluence being  exerted  by  these  bodies. 

More  mysterious,  if  possible,  than  any  of  the  facts 
we  have  discussed  is  the  phenomenon  of  magnetic 
storms.  The  needle  has  been  exhibiting  for  several 
weeks  the  most  perfect  uniformity  of  oscillation.  Day 
after  day,  the  careful  microscopic  observation  of  the 
needle's  progress  has  revealed  a  steady  swaying  to  and 
fro,  such  as  may  be  seen  in  the  masts  of  a  stately  ship 
at  anchor  on  the  scarce-heaving  breast  of  ocean.  Sud- 
denly a  change  is  noted  ;  irregular  jerking  movements 
are  perceptible,  totally  distinct  from  the  regular  peri- 
odic oscillations.  A  magnetic  storm  is  in  progress. 
But  where  is  the  centre  of  disturbance,  and  what  are 
the  limits  of  the  storm  ?  The  answer  is  remarkable. 
If  the  jerking  movements  observed  in  places  spread 
over  very  large  regions  of  the  earth — and  in  some  well- 
authenticated  cases  over  the  whole  earth — be  compared 
with  the  local  time,  it  is  found  that  (allowance  being 
made  for  difference  of  longitude)  they  occur  precisely 
at  tKe  same  instant.  The  magnetic  vibrations  thrill  in 
one  moment  through  the  whole  frame  of  our  earth ! 

But  a  very  singular  circumstance  is  observed  to 
characterize  these  magnetic  storms.  They  are  nearly 


THE  EARTH  A  MAGNET.  43 

always  observed  to  be  accompanied  by  the  exhibition 
of  the  aurora  in  high  latitudes,  northern  and  southern. 
Probably  they  never  happen  without  such  a  display ; 
but  numbers  of  auroras  escape  our  notice.  The  con- 
verse proposition,  however,  has  been  established  as  a 
universal  one.  "No  great  display  of  the  aurora  ever 
occurs  without  a  strongly-marked  magnetic  storm. 

Magnetic  storms  sometimes  last  for  several  hours  or 
even  days. 

Remembering  the  influence  which  the  sun  has 
been  found  to  exercise  upon  the  magnetic  needle,  the 
question  will  naturally  arise,  Has  the  sun  any  thing  to 
do  with  magnetic  storms  ?  We  have  clear  evidence 
that  he  has. 

On  the  1st  of  September,  1859,  Messrs.  Carrington 
and  Hodgson  were  observing  the  sun,  one  at  Oxford 
and  the  other  in  London.  Their  scrutiny  was  directed 
to  certain  large  spots  which,  at  that  time,  marked  the 
sun's  face.  Suddenly  a  bright  light  was  seen  by  each 
observer  to  break  out  on  the  sun's  surface  and  to  travel, 
slowly  in  appearance,  but  in  reality  at  the  rate  of 
about  7,000  miles  in  a  minute,  across  a  part  of  the 
solar  disk.  Kow  it  was  found  afterward  that  the  self- 
registering  magnetic  instruments  at  Kew  had  made  at 
that  very  instant  a  strongly -marked  jerk.  It  was 
learned  that  at  that  moment  a  magnetic  storm  pre- 
vailed at  the  West  Indies,  in  South  America,  and  in 
Australia.  The  signal-men  in  the  telegraph-stations  at 


44  LIGHT   SCIENCE  FOR  LEISURE  HOURS. 

"Washington  and  Philadelphia  received  strong  electric 
shocks  ;  the  pen  of  Bain's  telegraph  was  followed  by  a 
flame  of  tire  ;  and  in  Norway  the  telegraphic  machin- 
ery was  set  on  fire.  At  night  great  auroras  were  seen 
in  both  hemispheres.  It  is  impossible  not  to  connect 
these  startling  magnetic  indications  with  the  remark- 
able appearance  observed  upon  the  sun's  disk. 

But  there  is  other  evidence.  Magnetic  storms  pre- 
vail more  commonly  in  some  years  than  in  others.  In 
those  years  in  which  they  occur  most  frequently,  it  is 
found  that  the  ordinary  oscillations  of  the  magnetic 
needle  are  more  extensive  than  usual.  !N\)w,  when 
these  peculiarities  had  been  noticed  for  many  years,  it 
was  found  that  there  was  an  alternate  and  systematic 
increase  and  diminution  in  the  intensity  of  magnetic 
action,  and  that  the  period  of  the  variation  was  about 
eleven  years.  But  at  the  same  time,  a  diligent  observer 
had  been  recording  the  appearance  of  the  sun's  face 
from  day  to  day  and  from  year  to  year.  He  had  found 
that  the  solar  spots  are  in  some  years  more  freely  dis- 
played than  in  others.  And  he  had  determined  the 
period  in  which  the  spots  are  successively  presented 
with  maximum  frequency  to  be  about  eleven  years. 
On  a  comparison  of  the  two  sets  of  observations,  it  was 
found  (and  has  now  been  placed  beyond  a  doubt  by 
many  years  of  continued  observation)  that  magnetic 
perturbations  are  most  energetic  when  the  sun  is  most 
spotted,  and  vice  versa. 


OUR  CHIEF  TIMEPIECE  LOSING  TIME.  45 

For  so  remarkable  a  phenomenon  as  this  none  but 
a  cosmical  cause  can  suffice.  We  can  neither  say  that 
the  spots  cause  the  magnetic  storms,  nor  that  the  mag- 
netic storms  cause  the  spots.  We  must  seek  for  a 
cause  producing  at  once  both  sets  of  phenomena.  There 
is  as  yet  no  certainty  in  this  matter,  but  it  seems  as  if 
philosophers  would  soon  be  able  to  trace  in  the  dis- 
turbing action  of  the  planets  upon  the  solar  atmosphere 
the  cause  as  well  of  the  marked  period  of  eleven  years 
as  of  other  less  distinctly-marked  periods  which  a  dili- 
gent observation  of  solar  phenomena  is  beginning  to 
educe. 

(From  the  Cornhill  Magazine,  June,  1868.) 


OUR    CHIEF    TIMEPIECE   LOSING    TIME. 

A  DISTINGUISHED  French  astronomer,  author  of  one 
of  the  most  fascinating  works  on  popular  astronomy 
that  has  hitherto  appeared,  remarks  that  a  man  would 
be  looked  upon  as  a  maniac  who  should  speak  of  the 
influence  of  Jupiter's  moons  upon  the  cotton-trade. 
Yet,  as  he  proceeds  to  show,  there  is  an  easily-traced 
connection  between  the  ideas  which  appear  at  first 
sight  so  incongruous.  The  link  is  found  in  the  deter- 
mination of  celestial  longitude. 

Similarly,  what  would  be  thought  of  an  astronomer 
who,  regarding  thoughtfully  the  stately  motion  of  the 
sidereal  system,  as  exhibited  on  a  magnified,  and  there- 


46  LIGHT   SCIENCE  FOR   LEISURE   HOURS. 

fore  appreciable,  scale  by  a  powerful  telescope,  should 
speak  of  the  connection  between  this  movement  arid 
the  intrinsic  worth  of  a  sovereign  ?  The  natural 
thought  with  most  men  would  be  that  "  too  much 
learning  "  had  made  the  astronomer  mad.  Yet,  when 
we  come  to  inquire  closely  into  the  question  of  a  sov- 
ereign's intrinsic  value,  we  find  ourselves  led  to  the 
diurnal  motion  of  the  stars,  and  that  by  110  very  intri- 
cate path.  For,  What  is  a  sovereign  ?  A  coin  contain- 
ing so  many  grains  of  gold  mixed  with  so  many  grains 
of  alloy.  A  grain,  we  know,  is  the  weight  of  such  and 
such  a  volume  of  a  certain  standard  substance — that  is, 
so  many  cubic  inches,  or  parts  of  a  cubic  inch,  of  that 
substance.  But  what  is  an  inch  ?  It  is  determined, 
we  find,  as  a  certain  fraction  of  the  length  of  a  pendu- 
lum vibrating  seconds  in  the  latitude  of  London.  A 
second,  we  know,  is  a  certain  portion  of  a  mean  solar 
day,  and  is  practically  determined  by  a  reference  to 
what  is  called  a  sidereal  day — the  interval,  namely,  be- 
tween the  successive  passages  by  the  same  star  of  the 
celestial  meridian  of  any  fixed  place.  lliis  interval  is 
assumed  to  be  constant,  and  it  has  indeed  been  de- 
scribed as  the  "one  constant  element'"  known  to  as- 
tronomers. 

"We  find,  then,  that  there  is  a  connection,  and  a 
very  important  connection,  between  the  motion  of  the 
stars  and  our  measures,  not  merely  of  value,  but  of 
weight,  length,  volume,  and  time.  In  fact,  our  whole 


OUR   CHIEF  TIMEPIECE  LOSING  TIME.  47 

system  of  weights  and  measures  is  founded  on  the  ap- 
parent diurnal  motion  of  the  sidereal  system,  that  is, 
on  the  real  diurnal  rotation  of  the  earth.  We  may 
look  on  the  meridian-plane  in  which  the  great  transit- 
telescope  of  the  Greenwich  Observatory  is  made  to 
swing,  as  the  gigantic  hand  of  a  mighty  dial,  a  hand 
which,  extending  outward  among  the  stars,  traces  out 
for  us,  by  its  motion  among  them,  the  exact  progress 
of  time,  and  so  gives  us  the  means  of  weighing,  meas- 
uring, and  valuing  terrestrial  objects  with  an  exactitude 
which  is  at  present  leyond  our  wants. 

The  earth,  then,  is  our  "  chief  timepiece,"  and  it  is 
of  the  correctness  of  this  giant  clock  that  we  are  now 
to  speak. 

But  how  can  we  test  a  timepiece  whose  motions 
we  select  to  regulate  every  other  timepiece  ?  If  a  man 
sets  his  watch  every  morning  by  the  clock  at  West- 
minster, it  is  clearly  impossible  for  him  to  test  the  ac- 
curacy of  that  clock  by  the  motions  of  his  watch.  It 
would,  indeed,  be  possible  to  detect  any  gross  change 
of  rate ;  but,  for  the  purpose  of  illustration,  I  assume, 
what  is  indeed  the  case,  that  the  clock  is  very  accurate, 
and,  therefore,  that  minute  errors  only  are  to  be  looked 
for  even  in  long  intervals  of  time.  And,  just  as  the 
watch  set  by  a  clock  cannot  be  made  use  of  to  test  the 
clock  for  small  errors,  so  our  best  timepieces  cannot  be 
employed  to  detect  slow  variations,  if  any  such,  exist, 
in  the  earth's  rotation-period. 


48  LIGHT  SCIESTCE  FOR  LEISURE  HOURS. 

Sir  William  Ilerschel,  who  early  saw  the  impor- 
tance of  the  subject,  suggested  another  method.  Some 
of  the  planets  rotate  in  such  a  manner,  and  bear  such 
distinct  marks  upon  their  surface,  that  it  is  possible, 
by  a  series  of  observations  extending  over  a  long  inter- 
val of  time,  to  determine  the  length  of  their  rotation- 
period  within  a  second  or  two.  Supposing  their  rota- 
tion uniform,  we  at  once  obtain  an  accurate  measure 
of  time.  Supposing. their  rotation  not  uniform,  we 
obtain — (1)  a  hint  of  the  kind  of  change  we  are  look- 
ing for ;  and  (2),  by  the  comparison  of  two  or  more 
planets,  the  means  of  guessing  how  the  variation  is  to 
be  distributed  between  the  observed  planets  and  our 
own  earth. 

Unfortunately,  it  turned  out  that  Jupiter,  one  of 
the  planets  from  which  Herschel  expected  most,  does 
not  afford  us  exact  information — his  real  surface  beino; 

•  ^ 

always  veiled  by  his  dense  and  vapor-laden  atmosphere. 
Saturn,  Yenus,  and  Mercury,  are  similarly  circum- 
stanced, and  are  in  other  respects  unfavorable  objects 
for  this  sort  of  observation.  Mars  only,  of  all  the 
planets,  is  really  available.  Distinctly  marked  (in 
telescopes  of  sufficient  power)  with  continents  and 
oceans,  which  are  rarely  concealed  by  vapors,  this 
planet  is  in  other  respects  fortunately  situated.  For  it 
is  certain  that  whatever  variations  may  be  taking 
place  in  planetary  rotations  must  be  due  to  external 
agencies.  Now,  Saturn  and  Jupiter  have  their  satel- 


OUR   CHIEF  TIMEPIECE   LOSING  TIME.  49 

lites  to  influence  (perhaps  appreciably  in  long  intervals 
of  time)  their  rotation -movements.  Yenus  and  Mer- 
cury are  near  the  sun,  and  are  therefore  in  this  respect 
worse  off  than  the  earth,  whose  rotation  is  in  question. 
Mars,  on  the  other  hand,  farther  removed  than  we  are 
from  the  sun,  having  also  no  moon,  and  being  of  small 
dimensions  (a  very  important  point,  be  it  observed, 
since  the  tidal  action  of  the  sun  depends  on  the  dimen- 
sions of  a  planet),  is  likely  to  have  a  rotation-period 
all  but  absolutely  constant. 

Herschel  was  rather  unfortunate  in  his  observa- 
tions of  Mars.  Having  obtained  a  rough  approxima- 
tion from  Mars'  rotation  in  an  interval  of  two  days — 
this  rough  approximation  being,  as  it  happened,  only 
thirty-seven  seconds  in  excess  of  the  true  period — he 
proceeded  to  take  three  intervals  of  one  month  each. 
This  should  have  given  a  much  better  value,  but,  as 
it  happened,  the  mean  of  the  values  he  obtained  was 
forty-six  seconds  too  great.  He  then  took  a  period  of 
two  years,  and  being  misled  by  the  erroneous  values 
he  had  already  obtained,  he  missed  one  rotation,  get- 
ting a  value  two  minutes  too  great.  Thirty  years  ago, 
two  German  astronomers,  Beer  and  Madler,  tried  the 
same  problem,  and  taking  a  period  of  seven  years,  ob- 
tained a  value  which  exceeds  the  true  value  by  only 
one  second.  Another  German,  Kaiser,  by  combining 
more  observations,  obtained  a  value  which  is  within 
one-fifteenth  of  a  second  of  the  true  value.  But  a 


50  LIGHT   SCIENCE  FOR  LEISURE  HOURS. 

comparison  of  observations  extending  over  200  years 
lias  enabled  the  present  writer  to  obtain  a  value  winch 
he  considers  to  lie  one-hundredth  part  of  a  second  of 
the  truth.  This  value  for  Mars'  rotation-period  is  24: 
hours  37  minutes  22*74  seconds. 

Here,  then,  wre  have  a  result  so  accurate,  that  at 
some  future  time,  it  may  serve  to  test  the  earth's  rota- 
tion-period. We  have  compared  the  rotation-rate  of 
our  test-planet  with  the  earth's  rate  during  the  past 
200  years ;  and  therefore,  if  the  earth's  rate  vary  by 
more  than  one-hundredth  of  a  second  in  the  next  two 
or  three  hundred  years,  we  shall — or,  rather,  our  de- 
scendants will — begin  to  have  some  notion  of  the 
change  at  the  end  of  that  time. 

But,  in  the  mean  time,  mankind  being  impatient, 
and  not  willing  to  leave  to  a  distant  posterity  any 
question  which  can  possibly  be  answered  now,  astron- 
omers have  looked  around  them  for  information 
available  at  once  on  this  interesting  point.  The  search 
has  not  been  in  vain.  In  fact,  we  are  able  to  an- 
nounce, with  an  approach  to  positiveness,  that  our 
great  terrestrial  timepiece  is  actually  losing  time. 

In  our  moon  we  have  a  neighbor  which  has  long 
been  in  the  habit  of  answering  truthfully  questions 
addressed  to  her  by  astronomers.  Of  old,  she  told 
Newton  about  gravitation,  and  when  he  doubted,  and 
urged  contradictory  evidence  offered — as  men  in  his 
time  supposed — by  the  earth,  she  set  him  on  the  right 


OUR  CHIEF  TIMEPIECE  LOSING  TIME.  51 

track,  so  that  when  in  due  time  the  evidence  offered 
by  the  earth  was  corrected,  Newton  wTas  prepared  at 
once  to  accept  and  propound  the  noble  theory  which 
rendered  his  name  illustrious.  Again,  men  wished  to 
learn  the  true  shape  of  the  earth,  and  went  hither  and 
thither  measuring  its  globe  ;  but  the  moon,  meanwhile, 
told  the  astronomer  who  remained  at  home  a  truer 
tale.  They  sought  to  learn  the  earth's  distance  from 
the  sun,  and  from  this  and  that  point  they  turned  their 
telescopes  on  Yenus  in  transit ;  but  the  moon  has  set 
them  nearer  the  truth,  and  that  not  by  a  few  miles, 
but  by  3,000,000  or  more.  "We  shall  see  that  she  has 
had  something  to  say  about  our  great  terrestrial  time- 
piece. 

One  of  the  great  charms  of  the  science  of  astron- 
omy is,  that  it  enables  meu.  to  predict.  At  such  and 
such  an  hour,  the  astronomer  is  able  to  say,  a  celestial 
body  will  occupy  such  and  such  a  point  on  the  celes- 
tial sphere.  You  direct  a  telescope  toward  the  point 
named,  and  lo  !  at  the  given  instant  the  promised  orb 
sweeps  across  the  field  of  view.  Each  year  there  is 
issued  a  thick  octavo  volume  crowded  with  such  predic- 
tions, three  or  four  years  in  advance  of  the  events 
predicted  ;  and  these  predictions  are  accepted  with  as 
little  doubt  by  astronomers  as  if  they  were  the  records 
of  past  events. 

But  astronomers  are  not  only  able  to  predict — they 
can  also  trace  back  the  paths  of  the  celestial  bodies, 


52  LIGHT   SCIENCE  FOR  LEISURE  HOURS. 

and  say:  "At  such  and  such  a  long-past  epoch,  a  given 
star  or  planet  occupied  such  and  such  a  position  upon 
the  celestial  sphere."  But  how  are  they  to  verify  such 
a  statement  ?  It  is  clear  that,  in  general,  they  cannot 
do  so.  Those  who  are  able  to  appreciate  (or  better, 
to  make  use  of)  the  predictions  of  astronomy,  will, 
indeed,  very  readily  accord  a  full  measure  of  confidence 
to  calculations  of  past  events.  They  know  that  as- 
tronomy is  justly  named  the  most  exact  of  the  sciences, 
and  they  can  see  that  there  is  nothing,  in  the  nature 
of  things,  to  render  retrospection  more  difficult  than 
prevision.  But  there  are  hundreds  who  have  no  such 
experience  of  the  exactness  of  modern  astronomical 
methods — who  have,  on  the  contrary,  a  vague  notion 
that  modern  astronomy  is  merely  the  successor  of 
systems  now  exploded ;  perhaps  even  that  it  may  one 
day  have  to  make  way  in  its  turn  for  new  methods. 
And  if  all  other  men  were  willing  to  accept  the  cal- 
culations of  astronomers  respecting  long-past  events, 
astronomers  themselves  would  be  less  easily  satisfied. 
Long  experience  has  taught  them  that  the  detection  of 
error  is  the  most  fruitful  source  of  knowledge ;  there- 
fore, wherever  such  a  course  is  possible,  they  always 
gladly  submit  their  calculations  to  the  test  of  obser- 
vation. 

Now,  looking  backward  into  the  far  past,  it  is  only 
here  and  there  that  we  see  records  which  afford  means 
of  comparison  with  modern  calculations.  The  planets 


OUR   CHIEF  TIMEPIECE  LOSING  TIME.  53 

have  swept  on  in  their  courses  for  ages  with  none 
to  note  them.  Gradually,  observant  men  began  to 
notice  and  record  the  more  remarkable  phenomena. 
But  such  records,  made  with  very  insufficient  instru- 
mental means,  have  in  general  but  little  actual  value. 
It  has  been  found  easy  to  confirm  them  without  any 
special  regard  to  accuracy  of  calculation. 

Buc  there  is  one  class  of  phenomena  which  no 
inaccuracy  of  observation  can  very  greatly  affect.  A 
total  eclipse  of  the  sun  is  an  occurrence  so  remark- 
able, that  (1)  it  can  hardly  take  place  without  being 
recorded,  and  (2)  a  very  rough  record  will  suffice  to 
determine  the  particular  eclipse  referred  to.  Long 
intervals  elapse  between  successive  total  eclipses 
visible  at  the  same  place  on  the  earth's  surface ;  and 
even  partial  eclipses  of  noteworthy  extent  occur  but 
seldom  at  any  assigned  place.  Yery  early,  therefore, 
in  the  history  of  modern  astronomy,  the  suggestion 
was  made,  that  eclipses  recorded  by  ancient  historians 
should  be  calculated  retrospectively.  An  unexpected 
result  rewarded  the  undertaking:  it  was  found  that 
ancient  eclipses  could  not  be  fairly  accounted  for 
without  assigning  a  slower  motion  to  the  moon  in 
long-past  ages  than  she  has  at  present ! 

Here  was  a  difficulty  which  long  puzzled  mathe- 
maticians. One  after  another  was  foiled  by  it.  Halley, 
an  English  mathematician,  had  detected  the  difficulty, 
but  no  English  mathematician  was  able  to  grapple 


54  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

with  it.  Contented  with  Newton's  fame,  they  had 
suffered  their  Continental  rivals  to  shoot  far  ahead  in 
the  course  he  had  pointed  out.  But  the  best  Conti- 
nental mathematicians  were  defeated.  In  papers  of 
acknowledged  merit,  adorned  by  a  variety  of  new  pro- 
cesses, and  showing  a  deep  insight  into  the  question  at 
issue,  they  yet  arrived,  one  and  all,  at  the  same  con- 
clusion— failure. 

Ninety  years  elapsed  before  the  true  explanation 
was  offered  by  the  great  mathematician  Laplace.  A 
full  exposition  of  his  viewrs  would  be  out  of  place  in 
such  a  paper  as  the  present,  but  briefly,  they  amount 
to  this : 

The  moon  travels  in  her  orbit,  swayed  chiefly  by 
the  earth's  attraction.  But  the  sun,  though  greatly 
more  distant,  yet,  owing  to  the  immensity  of  his  mass, 
plays  an  important  part  in  guiding  our  satellite.  His 
influence  tends  to  relieve  the  moon,  in  part,  from  the 
earth's  sway.  Thus  she  travels  in  a  wider  orbit,  and 
with  a  slower  motion,  than  she  would  have  but  for  the 
sun's  influence.  Now,  the  earth  is  not  at  all  times 
equally  distant  from  the  sun,  and  his  influence  upon 
the  moon  is  accordingly  variable.  In  winter,  when  the 
earth  is  nearest  to  the  sun,  his  influence  is  greatest. 
The  lunar  month,  accordingly  (as  any  one  may  see  by 
referring  to  an  almanac),  is  longer  in  winter  than  in 
summer.  This  variation  had  long  been  recognized  as 
the  moon's  "  annual  equation ; "  but  Laplace  was  the 


OUR  CHIEF  TIMEPIECE   LOSING  TIME.  55 

first  to  point  out  that  the  variation  is  itself  slowly 
varying.  The  earth's  orbit  is  slowly  changing  in 
shape — becoming  more  and  more  nearly  circular  year 
by  year.  As  the  greater  axis  of  her  orbit  is  unchan- 
ging, it  is  clear  that  the  actual  extent  of  the  orbit  is 
slowly  increasing.  Thus,  the  moon  is  slightly  re- 
leased from  the  sun's  influence  year  by  year,  and  so 
brought  more  and  more  under  the  earth's  influence. 
She  travels,  therefore,  continually  faster  and  faster ; 
though  the  change  is  indeed  but  a  very  minute  one — 
only  to  be  detected  in  long  intervals  of  time.  Also* 
the  moon's  acceleration,  as  the  change  is  termed,  is 
only  temporary,  and  will  in  due  time  be  replaced  by 
an  equally  gradual  retardation. 

When  Laplace  had  calculated  the  extent  of  the 
change  due  to  the  cause  he  had  detected,  and  when  it 
was  found  that  ancient  eclipses  were  now  satisfactorily 
accounted  for,  it  may  well  be  believed  that  there  was 
triumph  in  the  mathematical  camp.  But  this  was  not 
all.  Other  mathematicians  attacked  the  same  problem, 
and  their  results  agreed  so  closely  that  all  were  con- 
vinced that  the  difficulty  was  thoroughly  vanquished. 

A  very  noteworthy  result  flowed  from  Laplace's 
calculations.  Among  other  solutions  which  had  been 
suggested,  was  the  supposition  (supported  by  no  less 
an  authority  than  Sir  Isaac  Newton,  who  lived  to  see 
the  commencement  of  the  long  conflict  maintained  by 
mathematicians  with  this  difficulty),  that  it  is  not  the 


56  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

moon  travelling  more  quickly,  but  our  earth  rotating 
more  slowly,  which  causes  the  observed  discrepancy. 
Now,  it  resulted  from  Laplace's  labors — as  he  was  the 
first  to  announce — that  the  period  of  the  earth's  rota- 
tion has  not  varied  by  one-tenth  of  a  second  per  century 
in  the  last  two  thousand  years.  The  question  thus 
satisfactorily  settled,  as  was  supposed,  was  shelved  for 
more  than  a  quarter  of  a  century.  The  rasult,  also, 
which  seemed  to  flow  from  the  discussion — the  con- 
stancy of  the  earth's  rotation-movement  —  was  ac- 
cepted ;  and,  as  we  have  seen,  our  national  system  of 
measures  was  founded  upon  the  assumed  constancy  of 
the  day's  duration. 

But  mathematicians  were  premature  in  their  re- 
joicings. The  question  has  been  brought,  by  the 
labors  of  Professor  Adams — co-discoverer  with  Le- 
verrier  of  the  distant  Neptune — almost  exactly  to  the 
point  which  it  occupied  a  century  ago.  We  are  face 
to  face  with  the  very  difficulties — somewhat  modified 
in  extent  but  not  in  character — which  puzzled  Halley, 
Euler,  and  Lagrange.  It  would  be  an  injustice  to  the 
memory  of  Laplace  to  say  that  his  labors  were  thrown 
away.  The  explanation  offered  by  him  is  indeed  a 
just  one,  but  it  is  insufficient.  Properly  estimated,  it 
removes  only  half  the  difficulty  which  had  perplexed 
mathematicians.  It  would  be  quite  impossible  to  pre- 
sent in  brief  space,  and  in  form  suited  to  these  pages, 
the  views  propounded  by  Adams.  What,  for  instance, 


OUR   CHIEF   TIMEPIECE   LOSING  TIME.  57 

would  most  of  our  readers  learn  if  we  were  to  tell  them 
that,  "  when  the  variability  of  the  eccentricity  is  taken 
into  account,  in  integrating  the  differential  equations 
involved  in  the  problem  of  the  lunar  motions — that  is, 
when  the  eccentricity  is  made  a  function  of  the  time 
— non-periodic  or  secular  terms  appear  in  the  expres- 
sion for  the  moon's  mean  motion  " — and  so  on  ?  Let  it 
suffice  to  say  that  Laplace  had  considered  only  the 
effect  of  the  sun  in  diminishing  the  earth's  pull  on  the 
moon,  supposing  that  the  slow  variation  in  the  sun's 
direct  influence  on  the  moon's  motion  in  her  orbit  must 
be  self-compensatory  in  long  intervals  of  time.  Adams 
has  shown,  on  the  contrary,  that  when  this  variation 
is  closely  examined,  no  such  compensation  is  found  to 
take  place ;  and  that  the  effect  of  this  want  of  com- 
pensation is  to  diminish  by  more  than  one-half  the 
effects  due  to  the  slow  variation  examined  by  Laplace. 
These  views  gave  rise  at  first  to  considerable  con- 
troversy. Pontecoulant  characterized  Adams's  pro- 
cesses as  "analytical  conjuring-tricks;"  and  Leverrier 
stood  up  gallantly  in  defence  of  Laplace.  The  contest 
swayed  hither  and  thither  for  a  while  ;  but  gradually 
the  press  of  new  arrivals  on  Adams's  side  began  to 
prevail.  One  by  one,  his  antagonists  gave  way ;  new 
processes  have  confirmed  his  results,  figure  for  figure ; 
and  no  doubt  now  exists,  in  the  mind  of  any  astron- 
omer competent  to  judge,  of  the  correctness  of  Ad- 


58  LIGHT   SCIENCE   FOR  LEISURE  HOURS. 

But  side  by  side  with  this  inquiry,  another  Lad 
been  in  progress.  A  crowd  of  diligent  laborers  had 
been  searching  with  close  and  rigid  scrutiny  into  the 
circumstances  attending  ancient  eclipses.  A  new  light 
had  been  thrown  upon  this  subject  by  the  labors  of 
modern  travellers  and  historians.  One  remarkable 
instance  of  this  may  be  cited.  Mr.  Layard  has  iden- 
tified the  site  of  Larissa  with  the  modern  Nimroud. 
]^ow,  Xenophon  relates  that  when  Larissa  was  besieged 
by  the  Persians,  an  eclipse  of  the  sun  took  place,  so 
remarkable  in  its  effects  (and  therefore  undoubtedly 
total),  that  the  Median  defenders  of  the  town  threw 
down  their  arms  and  the  city  was  accordingly  cap- 
tured. And  Hansen  had  shown  that  a  certain  estimate 
of  the  moon's  motion  makes  the  eclipse  which  occurred 
on  August  15,  310  B.  c.,  not  only  total,  but  central  at 
Mmroud.  Some  other  remarkable  eclipses — as  the 
celebrated  sunset  eclipse  (total)  at  Rome  399  u.  c., 
the  eclipse  which  enveloped  the  fleet  of  Agathocles 
as  he  escaped  from  Syracuse;  the  famous  eclipse  of 
Thales,  which  interrupted  a  battle  between  the  Medes 
and  Lydians;  and  even  the  partial  eclipse  which 
(probably)  caused  the  "going  back  of  the  shadow  upon 
the  dial  of  Ahaz  " — have  all  been  accounted  for  satis, 
factorily  by  Hansen's  estimate  of  the  moon's  motion ; 
so,  also,  have  nineteen  lunar  eclipses  recorded  in  the 
Almagest. 

This  estimate  of  Hansen's,  which  accounts  so  satis- 


OUR   CHIEF   TIMEPIECE   LOSING  TIME.  59 

factorily  for  solar  and  hmar  eclipses,  makes  the  moon's 
rate  of  motion  increase  more  than  twice  as  fast  as  it 
should  do  according  to  the  calculations  of  Adams. 
But  before  our  readers  run  away  with  the  notion  that 
astronomers  have  here  gone  quite  astray,  it  will  be 
well  to  present,  in  a  simple  manner,  the  extreme 
minuteness  of  the  discrepancy  about  which  all  the  coil 
has  been  made. 

Suppose  that,  just  in  front  of  our  moon,  a  false  moon 
exactly  equal  to  ours  in  size  and  appearance  (see  note 
at  the  end  of  this  paper)  were  to  set  oft'  with  a  motion 
corresponding  to  the  present  motion  of  the  moon,  save 
only  in  one  respect — namely,  that  the  false  moon's 
motion  should  not  be  subject  to  Ihe  change  we  are 
considering,  termed  the  acceleration.  Then  one  hun- 
dred years  would  elapse  before  our  moon  would  fairly 
begin  to  show  in  advance.  She  would,  in  that  time, 
have  brought  only  one-one-huudred-and-fiftieth  part 
of  her  breadth  from  behind  the  false  moon.  At  the 
end  of  another  century,  she  would  have  gained  four 
times  as  much ;  at  the  end  of  a  third,  nine  times  as 
much  :  and  so  on.  She  would  not  fairly  have  cleared 
her  own  breadth  in  less  than  twelve  hundred  years. 
But  the  whole  of  this  gain,  minute  as  it  is,  is  not  left 
unaccounted  for  by  our  modern  astronomical  theories. 
Half  the  gain  is  explained,  the  other  half  remains  to 
be  interpreted ;  in  other  words,  the  moon  travels  far- 
ther by  about  half  her  own  breadth  in  twelve  cen- 


GO  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

turics   than   she  should    do  according  to  the    lunar 
theory. 

But  in  this  difficulty,  small  as  it  seems,  we  are  not 
left  wholly  without  resource.  We  are  not  only  able 
to  say  that  the  discrepancy  is  probably  due  to  a 
gradual  retardation  of  the  earth's  rotation-movement, 
but  we  are  able  to  place  our  finger  on  a  very  sufficient 
cause  for  such  a  retardation.  One  of  the  most  firmly- 
established  principles  of  modern  science  is  this — that 
where  work  is  done,  force  is,  in  some  way  or  other, 
expended.  The  doing  of  work  may  show  itself  in  a 
variety  of  ways — in  the  generation  of  heat,  in  the 
production  of  light,  in  the  raising  of  weights,  and  so 
on ;  but  in  every  case  an  equivalent  force  must  be 
expended.  If  the  brakes  are  applied  to  a  train  in 
motion,  intense  heat  is  generated  in  the  substance  of 
the  brake ;  now,  the  force  employed  by  the  brakesman 
is  not  equivalent  to  the  heat  generated.  "Where,  then, 
is  the  balance  of  force  expended  ?  We  all  know  that 
the  train's  motion  is  retarded,  and  this  loss  of  motion 
represents  the  requisite  expenditure  of  force.  !N"ow,  is 
there  any  process  in  Nature  resembling,  in  however 
remote  a  degree,  the  application  of  a  brake  to  check 
the  earth's  rotation  ?  There  is.  The  tidal  wave,  which 
sweeps,  twice  a  day,  round  the  earth,  travels  in  a  di- 
rection contrary  to  the  earth's  motion  of  rotation. 
That  this  wave  "  does  work,"  no  one  can  doubt  who 
has  watched  its  effects.  The  mere  rise  and  fall  in 


OUR  CHIEF  TIMEPIECE   LOSING  TIME.  61 

open  ocean  may  not  be  strikingly  indicative  of  "  work 
done ; "  but  when  we  see  the  behavior  of  the  tidal 
wave  in  narrow  channels,  when  we  see  heavily-laden 
ships  swept  steadily  up  our  tidal  rivers,  we  cannot  but 
recognize  the  expenditure  of  force.  Now,  where  does 
this  force  come  from  ?  Motion  being  the  great  "  force- 
measurer,"  what  motion  suffers  that  the  tides  may 
-work  ?  AVe  may  securely  reply,  that  the  only  motion 
which  can  supply  the  requisite  force  is  the  earth's 
motion  of  rotation.  Therefore,  it  is  no  idle  dream, 
but  a  matter  of  absolute  certainty,  that,  though  slowly, 
still  very  surely,  our  terrestrial  globe  is  losing  its  rota- 
tion-movement. 

Considered  as  a  timepiece,  what  are  the  earth's 
errors?  Suppose,  for  a  moment,  that  the  earth  was 
tinned  and  rated  two  thousand  years  ago,  how  much 
has  she  lost,  and  what  is  her  "  rate  error  ? "  She  has 
lost  in  that  interval  nearly  one  hour  and  a  quarter,  and 
she  is  losing  now  at  the  rate  of  one  second  in  twelve 
weeks.  In  other  words,  the  length  of  a  day  is  now 
more  by  about  one-eighty-fourth  part  of  a  second  than 
it  was  two  thousand  years  ago.  At  this  rate  of  change, 
our  day  would  merge  into  a  lunar  month  in  the  course 
of  thirty-six  thousand  millions  of  years.  But  after  a 
while,  the  change  will  take  place  more  slowly,  and 
some  trillion  or  so  of  years  will  elapse  before  the  full 
change  is  effected. 

Distant,  however,  as  is  the   epoch  at  which  the 


62  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

changes  we  have  been  considering  will  become  effec- 
tive, the  subject  appears  to  us  to  have  an  interest  apart 
from  the  mere  speculative  consideration  of  the  future 
physical  condition  of  our  globe.  Instead  of  the  recur- 
rence of  ever-varying,  closely-intermingled  cycles  of 
fluctuation,  we  see,  now  for  the  first  time,  the  evidence 
of  cosmical  decay — a  decay  which,  in  its  slow  progress, 
may  be  but  the  preparation  for  renewed  genesis — but 
still,  a  decay  which,  so  far  as  the  races  at  present  sub- 
sisting upon  the  earth  are  concerned,  must  be  looked 
upon  as  finally  and  completely  destructive.* 

(From  Chambers' s  Journal,  October  12,  1867.) 


ENCKE  THE  ASTRONOMER. 

FOUK  years  have  passed  since  Encke  died.  Even 
those  four  years  have  witnessed  notable  changes  in  the 
aspect  of  the  science  lie  loved  so  well.  But  we  must 
look  back  over  more  than  fifty  years,  if  we  would  form 
an  estimate  of  the  position  of  astronomy  when  Encke's 
most  notable  work  was  achieved.  At  Seeberge,  under 
Lindenau,  Encke  had  been  perfecting  himself  in  the 

*  In  the  Quarterly  Journal  of  Science  for  October,  1866,  a  more 
detailed  but  somewhat  less  popular  account  of  the  subject  of  the  above 
paper  is  presented.  A  few  months  earlier,  a  charmingly-written  paper 
on  the  same  subject,  from  the  pen  of  Mr.  J.  M.  Wilson,  of  Rugby,  had 
appeared  in  the  Eagle,  a  magazine  written  by  and  for  members  of  St. 
John's  College,  Cambridge.  Although  my  paper  in  the  Quarterly  Journal 
of  Science  was  written  quite  independently  of  Mr.  Wilson's  (which, 
however,  I  had  read),  yet  it  chanced  that  in  dessribing  the  same  mathe- 


ENCKE  THE  ASTRONOMER.  03 

higher  branches  of  mathematical  calculation.  He  took 
the  difficult  work  of  determining  the  orbital  motions 
of  newly-discovered  comets  under  his  special  charge, 
and  Dr.  Bruhns  tells  us  that  every  comet  which  was 
detected  during  Encke's  stay  at  Seeberge  was  subjected 
to  rigid  scrutiny  by  the  indefatigable  mathematician. 
Before  long  a  discovery  of  the  utmost  importance 
rewarded  his  persevering  labors.  Pons  had  detected 
on  November  26,  1818,  a  comet  of  no  very  brilliant 
aspect,  which  was  watched  first  at  Marseilles,  and  then 
at  Mannheim,  until  December  29th.  Encke  next  took  up 

matical  relations,  and  the  same  sequence  of  events,  I  here  and  there 
used  language  closely  resembling  his.  I  fear  this  led  for  a  while  to  some 
misconception ;  but  I  was  fortunately  able  to  show  in  Mr.  De  la  Rue's 
address  to  the  Astronomical  Society,  on  the  same  subject,  passages  yet 
more  strikingly  resembling  some  in  Mr.  Wilson's  paper  (written  sub- 
sequently and  quite  independently).  The  fact  would  seem  to  be  that,  if 
two  persons  describe  the  same  events,  and  deal  with  the  same  mathe- 
matical relations,  it  is  almost  certain  that  in  more  than  one  passage  they 
will  use  somewhat  similar  expressions. 

I  was  actually  indebted  to  Mr.  Wilson's  paper  for  one  illustration, 
however— that  derived  from  the  movements  of  a  supposed  artificial 
moon ;  and  I  think  that,  had  his  paper  appeared  in  a  magazine  printed 
for  general  circulation,  I  should  have  referred  to  it.  As  it  was,  this 
seemed  useless  so  far  as  the  readers  of  the  Quarterly  Journal  of  Science 
were  concerned.  The  circumstances  of  the  case  were,  indeed,  far 
from  calling  for  a  reference ;  while  I  had  in  a  sense  made  the  illustra- 
tion my  own  by  detecting  an  important  miscalculation  in  the  original 
(the  amount  of  advance  being  either  doubled  or  halved — I  forget  which). 
Had  I  referred  to  Mr.  Wilson's  paper,  I  must  needs  have  mentioned 
this  mistake ;  and  it  would  have  appeared  as  though  I  had  no  other 
purpose  in  making  the  reference. 

I  mention  these  matters  to  explain  what  I  fear  my  esteemed  fellow- 
collegian  was  disposed  at  the  time  to  regard  as  either  a  wrong  or  a 
slight.  Nothing  was  further  from  my  intention  than  either. 


G4  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

the  work,  and  tracked  the  comet  until  January  12th. 
Combining  the  observations  made  between  December 
22d  and  January  12th,  he  assigned  to  the  body  apara- 
bolic  orbit.  But  he  was  not  satisfied  with  the  accord- 
ance between  this  path  and  the  observed  motions  of  the 
body.  "When  he  attempted  to  account  for  the  motions 
of  the  comet  by  means  of  an  orbit  of  comparatively 
short  period,  he  was  struck  by  the  resemblance  between 
the  path  thus  deduced  and  that  of  Comet  I,  1805. 
Gradually  the  idea  dawned  upon  him  that  a  new  era 
was  opening  for  science.  Hitherto  the  only  periodical 
comets  which  had  been  discovered  except  Lexell's — 
the  "lost  comet" — had  travelled  in  orbits  extending 
far  out  into  space  beyond  the  paths  of  the  most  distant 
known  planets.  But  now  Encke  saw  reason  to  believe 
that  he  had  to  deal  with  a  comet  travelling  within  the 
orbit  of  Jupiter.  On  February  5th,  he  wrote  to  the 
eminent  mathematician  Gauss,  pointing  out  the  results 
of  his  inquiries,  and  saying  that  he  only  waited  for  the 
encouragement  and  authority  of  his  former  teacher  to 
prosecute  his  researches  to  the  end  toward  which  they 
already  seemed  to  point.  Gauss,  in  reply,  not  only 
encouraged  Encke  to  proceed,  but  counselled  him  as 
to  the  course  he  should  pursue.  The  result  we  all 
know.  Encke  showed  conclusively  that  the  newly- 
discovered  comet  travels  in  a  path  of  short  period,  and 
that  it  had  already  made  its  appearance  several  times 
in  our  neighborhood. 


EXCKE  THE  ASTRONOMER.  65 

From  the  date  of  this  discovery,  Encke  took  high 
rank  among  the  astronomers  of  Europe.  His  subse- 
quent labors  by  no  means  fell  short  of  the  promise 
which  this,  his  first  notable  achievement,  had  aiforded. 
If  he  effected  less  as  an  astronomical  observer  than 
many  of  his  contemporaries,  he  was  surpassed  by 
few  as  a  manipulator  of  those  abstruse  formulae  by 
which  the  planetary  perturbations  are  calculated.  It 
was  to  the  confidence  engendered  by  this  skill  that  we 
owe  his  celebrated  discovery  of  the  acceleration  of  the 
motion  of  the  comet  mentioned  above.  Assured  that 
he  had  rightly  estimated  the  disturbances  to  which 
the  comet  is  subjected,  he  was  able  to  pronounce  con- 
fidently that  some  cause  continually  (though  all  but  im- 
perceptibly) impedes  the  passage  of  this  body  through 
space,  and  so — by  one  of  those  strange  relations  which 
the  student  of  astronomy  is  familiar  with — the  contin- 
ually retarded  comet  travels  ever  mores  wiftly  along  a 
continually  diminishing  orbit. 

Bruhns's  Life  of  Encke  is  well  worth  reading,  not 
only  by  those  who  are  interested  in  Encke's  fame  and 
work  as  an  astronomer,  but  by  the  general  reader. 
Encke  the  man  is  presented  to  our  view,  as  well  as 
Encke  the  astronomer.  "With  loving  pains  the  pupil 
of  the  great  astronomer  handles  the  theme  he  has 
selected.  The  boyhood  of  Encke,  his  studies,  his 
soldier-life  in  the  great  uprising  against  Napoleon  in 
1813,  and  his  work  at  the  Seeberge  Observatory ;  his 


66  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

labors  on  comets  and  asteroids ;  his  investigations  of 
the  transits  of  1T61  and  1769  ;  his  life  as  an  acade- 
mician, and  as  director  of  an  important  observatory ; 
his  orations  at  festival  and  funeral ;  and  lastly,  his 
illness  and  death,  are  described  in  these  pages  by  one 
who  held  Encke  in  grateful  remembrance  as  "  teacher 
and  master,"  and  as  "  a  fatherly  friend." 

Xot  the  least  interesting  feature  of  the  work  is  the 
correspondence  introduced  into  its  pages.  We  find 
Encke  in  communication  with  Humboldt,  with  Bessel 
and  Struve,  with  Hansen,  Olbers,  and  Argelander; 
with  a  host,  in  fine,  of  living  as  well  as  of  departed 
men  of  science. 

CFrom  Nature,  March  10,  1870.) 


VENUS    ON  THE  SUN'S  FACE. 

MOKE  than  a  century  ago  scientific  men  were  look- 
ing forward  with  eager  interest  to  the  passage  of  the 
planet  Yenus  across  the  sun's  face  in  1769.  The 
Royal  Society  judged  the  approaching  event  to  be  of 
such  extreme  importance  to  the  science  of  astronomy, 
that  they  presented  a  memorial  to  King  George  III., 
requesting  that  a  vessel  might  be  fitted  out,  at  govern- 
ment expense,  to  convey  skilful  observers  to  one  of  the 
stations  which  had  been  judged  suitable  for  observing 
the  phenomenon.  The  petition  was  complied  with, 


VENUS  OX  THE  SUN'S  FACE.  67 

and,  after  some  difficulty  as  to  the  choice  of  a  leader, 
the  good  ship  "  Endeavor,"  of  370  tons,  was  placed 
under  the  command  of  Captain  Cook.  The  astro- 
nomical work  intrusted  to  the  expedition  was  com- 
pletely successful ;  and  thus  it  was  held  that  England 
had  satisfactorily  discharged  her  part  of  the  work  of 
utilizing  the  rare  phenomenon  known  as  a  transit  of 
Yen  us. 

A  century  passes,  and  science  is" again  awaiting  with 
interest  the  approach  of  one  of  these  transits.  But  now 
her  demands  are  enlarged.  It  is  not  one  ship  that  is 
asked  for,  but  the  full  cost  and  charge  of  several  ex- 
peditions. And  this  time,  also,  science  has  been  more 
careful  in  taking  time  by  the  forelock.  The  first  hints 
of  her  requirements  were  heard  some  fourteen  years 
ago,  when  the  Astronomer-Royal  began  that  process, 
of  laborious  inquiry  which  a  question  of  this  sort  neces- 
sarily demands.  Gradually,  her  hints  became  more 
and  more  plain-spoken  ;  insomuch  that  Mr.  Airy — her 
mouth-piece  in  this  case — stated  definitely,  a  few  months 
ago,  what  he  thought  science  had  a  right  to  claim  from 
England  in  this  matter.  When  the  claim  came  before 
our  government,  it  was  met  with  a  liberality  which 
was  a  pleasing  surprise  after  Mr.  Lowe's  placid  refer- 
ence of  scientific  people  to  their  own  devices.  The 
sum  of  ten  thousand  five  hundred  pounds  has  been 
granted  to  meet  the  cost  of  several  important  and  well- 
appointed  expeditions  ;  and  doubtless  further  material 


68  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

aid  will  be  derived  from  the  various  government  ob- 
servatories. 

And  now  let  us  inquire  why  so  much  interest  is  at- 
tached to  a  phenomenon  which  appears,  at  first  sight, 
to  be  so  insignificant.  Transits,  eclipses,  and  other 
phenomena  of  that  nature,  are  continually  occurring, 
without  any  particular  interest  being  attached  to  them. 
The  telescopist  may  see  half  a  dozen  such  phenomena 
in  the  course  of  a  night  or  two,  by  simply  watching 
the  satellites  of  Jupiter,  or  the  passage  of  our  moon 
over  the  stars.  Even  the  great  eclipse  of  1868  did 
not  attract  so  much  interest  as  the  coming  transit  of 
Yenus,  yet  that  eclipse  had  never  been  equalled  in  im- 
portance by  any  which  has  occurred  in  historic  times, 
and  hundreds  of  years  must  pass  before  such  another 
happens,  whereas  transits  of  Venus  are  far  from  being 
so  uncommon. 

The  fact  is,  that  Yenus  gives  us  the  best  means  we 
have  of  mastering  a  problem  which  is  one  of  the  most 
important  within  the  whole  range  of  the  science  of 
astronomy.  "We  use  the  term  important,  of  course, 
with  reference  to  the  scientific  significance  and  interest 
of  the  problem.  Practically,  it  matters  little  to  us 
whether  the  sun  is  a  million  of  miles  or  a  thousand 
millions  of  miles  from  us.  The  subject  must  in  any 
case  be  looked  upon  as  an  extra-parochial  one.  But 
science  does  occasionally  attach  immense  interest  to 
extra-parochial  subjects.  And  this  is  neither  unwise 


VENUS  ON  THE  SUN'S  FACE.  69 

nor  unreasonable,  since  we  find  implanted  in  our  very 
nature — and  not  merely  in  the  nature  of  scientific  men 
— a  quality  which  causes  us  to  take  interest  in  a  variety 
of  matters  that  do  not  in  the  least  concern  our  personal 
interests.  Nor  is  this  quality,  rightly  considered,  one 
of  the  least  noble  characteristics  of  the  human  race. 

That  the  determination  of  the  sun's  distance  is  im- 
portant, in  an  astronomical  sense,  will  be  seen  at  once 
when  it  is  remembered  that  the  ideas  we  form  of  the 
dimensions  of  the  solar  system  are  wholly  dependent 
oil  our  estimate  of  the  sun's  distance.  Nor  can  we 
gauge  the  celestial  depths  with  any  feeling  of  assur- 
ance, unless  we  know  the  true  length  of  that  which  is 
our  sole  measuring-rod.  It  is,  in  fact,  our  basis  of 
measurement  for  the  whole  visible  universe.  In  some 
respects,  even  if  we  knew  the  sun's  distance  exactly, 
it  would  still  be  an  unsatisfactory  gauge  for  the  stellar 
depths.  But  that  is  the  misfortune,  not  the  fault  of 
the  astronomer,  who  must  be  content  to  use  the  meas- 
uring-rod which  Nature  gives  him.  All  he  can  do  is 
to  find  out  as  nearly  as  he  can  its  true  length. 

"When  we  come  to  consider  how  the  astronomer  is 
to  determine  this  very  element — the  sun's  distance — we 
find  that  he  is  hampered  with  a  difficulty  of  precisely 
the  same  character. 

The  sun  being  an  inaccessible  object,  the  astronomer 
can  app]y  no  other  methods  to  determine  its  distance — 
directly — than  those  which  a  surveyor  would  use  in 


70  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

determining  the  distance  of  an  inaccessible  castle,  or 
rock,  or  tree,  or  the  like.  We  snail  see  presently  that 
the  ingenuity  of  astronomers  has,  in  fact,  suggested 
some  other  indirect  methods.  But  clearly  the  most 
satisfactory  estimate  we  can  have  of  the  sun's  distance 
is  one  founded  on  such  simple  notions  and  involving  in 
the  main  such  processes  of  calculation  as  we  have  to 
deal  with  in  ordinary  surveying. 

There  is,  in  this  respect,  no  mystery  about  the  so- 
lution of  the  famous  problem.  Unfortunately,  there  is 
enormous  difficulty. 

When  a  surveyor  has  to  determine  the  distance  of 
an  inaccessible  object,  he  proceeds  in  the  following 
manner :  He  first  very  carefully  measures  a  base-line 
of  convenient  length.  Then  from  either  end  of  the 
base-line  he  takes  the  bearings  of  the  inaccessible  ob- 
ject— that  is,  he  observes  the  direction  in  which  it  lies. 
It  is  clear  that,  if  he  were  now  to  draw  a  figure  on 
paper,  laying  down  the  base-line  to  some  convenient 
scale,  and  drawing  lines  from  its  ends  in  directions 
corresponding  to  the  bearings  of  the  observed  object, 
these  lines  would  indicate,  by  their  intersection,  the 
true  relative  position  of  the  object.  In  practice,  the 
mathematician  does  not  trust  to  so  rough  a  method  as 
construction,  but  applies  processes  of  calculation. 

Now,  it  is  clear  that  in  this  plan  every  thing  de- 
pends on  the  base-line.  It  must  not  be  too  short  in 
comparison  with  the  distance  of  the  inaccessible  object ; 


VENUS  ON  THE  SUN'S  FACE.  71 

for  then,  if  we  make  the  least  error  in  observing  the 
bearings  of  the  object,  we  get  an  important  error  in 
the  resulting  determination  of  the  distances.  The 
reader  can  easily  convince  himself  of  this  by  drawing 
an  illustrative  case  or  two  on  paper. 

The  astronomer  has  to  take  his  base-line  for  deter- 
mining the  sun's  distance,  upon  our  earth,  which  is 
quite  a  tiny  speck  in  comparison  with  the  vast  distance 
which  separates  us  from  the  sun.  It  had  been  found 
difficult  enough  to  determine  the  moon's  distance  with 
such  a  short  base-line  to  work  from.  But  the  moon  is 
only  about  a  quarter  of  a  million  of  miles  from  us, 
while  the  sun  is  more  than  ninety  millions  of  miles  off. 
Thus  the  problem  was  made  several  hundred  times 
more  difficult — or,  to  speak  more  correctly,  it  was 
rendered  simply  insoluble  unless  the  astronomer  could 
devise  some  mode  of  observing  which  should  vastly 
enhance  the  power  of  his  instruments. 

For,  let  us  consider  an  illustrative  case.  Suppose 
there  were  a  steeple  five  miles  off,  and  we  had  a  base- 
line only  two  feet  long.  That  would  correspond  as 
nearly  as  possible  to  the  case  the  astronomer  has  to 
deal  with.  Now,  what  change  of  direction  could  be 
observed  in  the  steeple  by  merely  shifting  the  eye 
along  a  line  of  two  feet  ?  There  is  a  ready  way  of 
answering.  Invert  the  matter.  Consider  what  a  line 
of  two  feet  long  would  look  like  if  viewed  from  a  dis- 
tance of  five  miles.  Would  its  length  be  appreciable, 


72  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

to  say  nothing  of  its  being  measurable  ?  Yet  it  is  just 
sucli  a  problem  as  the  measurement  of  that  line  which 
the  astronomer  would  have  to  solve. 

But  even  this  is  not  all.  In  our  illustration  only 
one  observer  is  concerned,  and  he  would  be  able  to  use 
one  set  of  instruments.  Suppose,  however,  that  from 
one  end  of  the  two-feet  line  an  observer  using  one  set 
of  instruments  took  the  bearing  of  the  steeple;  and 
that,  half  a  year  after,  another  observer  brought  an- 
other set  of  instruments  and  took  the  bearing  of  the 
steeple  from  the  other  end  of  the  two-feet  line,  is  it  not 
obvious  how  enormously  the  uncertainty  of  the  result 
wrould  be  increased  by  such  an  arrangement  as  this  ? 
One  observer  would  have  his  own  peculiar  powers  of 
observation,  his  own  peculiar  weaknesses;  the  other 
would  have  different  peculiarities.  One  set  of  instru- 
ments would  be  characterized  by  its  own  faults  or 
merits,  so  would  the  other.  One  series  of  observa- 
tions would  be  made  in  summer,  with  all  the  dis- 
turbing effects  due  to  heat ;  the  other  would  be  made 
in  winter,  with  all  the  disturbing  effects  due  to 
cold. 

The  observation  of  the  sun  is  characterized  by  all 
these  difficulties.  Limited  to  the  base-lines  he  can 
measure  on  earth,  the  astronomer  must  set  one  ob- 
server in  one  hemisphere,  another  in  the  other.  Each 
observer  must  have  his  own  set  of  instruments ;  and 
every  observation  which  one  has  made  in  summer  will 


VENUS  ON  THE  SUN'S  FACE.  73 

have  to  be  compared  with  an  observation  which  the 
other  has  made  in  winter. 

Thus,  we  can  understand  that  astronomers  should 
have  failed  totally  when  they  attempted  to  determine 
the  sun's  distance  without  aid  from  the  other  celestial 
bodies. 

It  may  seem  at  first  sight  as  though  nothing  the 
other  celestial  bodies  could  tell  the  astronomer  would 
be  of  the  least  use  to  him,  since  these  bodies  are  for 
the  most  part  farther  off  than  the  sun,  and  even  those 
which  approach  nearest  to  us  are  still  far  beyond  the 
limits  of  distance  within  which  the  simple  plan  fol- 
lowed by  surveyors  could  be  of  any  service.  And 
besides,  it  might  be  supposed  that  information  about 
the  distance  of  one  celestial  body  could  be  of  no  partic- 
ular service  toward  the  determination  of  the  distance 
of  another. 

But  two  things  aid  the  astronomer  at  this  point : 
First  of  all,  he  has  discovered  the  law  which  associates 
together  the  distances  of  all  the  planets  from  the  sun  ; 
so  that  if  he  can  determine  the  distance  of  any  one 
planet  he  learns  immediately  the  distances  of  all.  Sec- 
ondly, the  planets  in  their  motion  travel  occasionally 
into  such  positions  that  they  become  mighty  indices, 
tracing  out  on  a  natural  dial-plate  the  significant  les- 
son from  which  the  astronomer  hopes  to  learn  so  much. 
To  take  an  instance  from  the  motions  of  another  planet 
than  the  one  we  are  dealing  with.  Mars  comes  some- 

4 


74  LIGHT   SCIENCE  FOR  LEISURE  HOURS. 

times  so  near  the  earth  that  the  distance  separating  us 
from  him  is  little  more  than  one-third  of  that  which 
separates  us  from  the  sun.  Suppose  that,  at  such  a 
time,  he  is  seen  quite  close  to  a  fixed  star.  That  star 
gives  the  astronomer  powerful  aid  in  determining  the 
planet's  distance.  For,  to  observers  in  some  parts  of 
the  earth,  the  planet  will  seem  nearer  to  the  star  than 
he  will  to  observers  elsewhere.  A  careful  comparison 
of  the  effects  thus  exhibited  will  give  significant  evi- 
dence respecting  the  distance  of  Mars.  And  we  see 
that  the  star  has  served  as  a  fixed  mark  upon  the  vast 
natural  dial  of  the  heavens,  just  as  the  division-marks 
on  a  clock-face  serve  to  indicate  the  position  of  the 
hands. 

JSTow,  we  can  at  once  see  why  Venus  holds  so  im- 
portant a  position  in  this  sort  of  inquiry.  Yen  us  is 
our  nearest  neighbor  among  the  planets.  She  comes 
several  millions  of  miles  nearer  to  us  than  Mars,  our 
next  neighbor  on  the  other  side.  That  is  the  primary 
reason  of  her  being  so  much  considered  by  astronomers. 
But  there  is  another  of  equal  importance.  Yenus 
travels  nearer  than  our  earth  to  the  sun.  And  thus 
there  are  occasions  when  she  gets  directly  between  the 
earth  and  the  sun.  At  those  times  she  is  seen  upon 
his  face,  and  his  face  serves  as  a  dial-plate  by  which  to 
measure  her  movements.  "When  an  observer  at  one 
part  of  the  earth  sees  her  on  one  part  of  the  sun's  face, 
another  observer  at  some  other  part  of  the  earth  will 


VENUS  ON  THE  SUN'S  FACE.  75 

see  her  on  another,  and  the  difference  of  position,  if 
accurately  measured,  would  at  once  indicate  the  sun's 
distance.  As  a  matter  of  fact,  other  modes  of  reading 
off  the  indications  of  the  great  dial-plate  have  to  be 
adopted.  Before  proceeding  to  consider  those  modes, 
however,  we  must  deal  with  one  or  two  facts  about 
Yenus's  movements  which  largely  affect  the  question 
at  issue. 

Let  us  first  see  what  we  gain  by  considering  the 
distance  of  Venus  rather  than  that  of  the  sun. 

At  the  time  of  a  transit  Yenus  is  of  course  on  a  line 
between  the  earth  and  the  sun,  and  she  is  at  somewhat 
less  than  a  third  of  the  sun's  distance  from  us.  Thus 
whatever  effect  an  observer's  change  of  place  would 
produce  upon  the  sun  would  be  more  than  trebled  in 
the  case  of  Yenus.  But  it  must  not  be  forgotten  that 
w^e  are  to  judge  the  motions  of  Yenus  by  means  of  the 
dial- plate  formed  by  the  solar  disk,  arid  that  dial-plate 
is  itself  shifted  as  the  observer  shifts  his  place.  Yenus 
is  shifted  three  times  as  much,  it  is  true ;  but  it  is  only 
the  balance  of  change  that  our  astronomer  can  rec- 
ognize. That  balance  is,  of  course,  rather  more  than 
twice  as  great  as  the  sun's  change  of  place. 

So  far,  then,  we  have  not  gained  much,  since  it  has 
been  already  mentioned  that  the  sun's  change  of  place 
is  not  measurable  by  any  process  of  observation  astron- 
omers can  apply. 

It  is  to  the  fact  that  we  have  the  sun's  disk  whereby 


76  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

to  measure  the  change  that  we  must  chiefly  trust ;  and 
even  that  would  be  insufficient  were  it  not  for  the  fact 
that  Yenus  is  not  at  rest,  but  travels  athwart  the  great 
solar  dial-plate.  We  are  thus  enabled  to  make  a  time 
measurement  take  the  place  of  a  measurement  of  space. 
If  an  observer  in  one  place  sees  Yenus  cross  the  sun's 
face  at  a  certain  distance  from  the  centre,  while  an 
observer  at  another  place  sees  her  follow  a  path  slight- 
ly farther  from  the  centre,  the  transit  will  clearly  seem 
longer  to  the  former  observer  than  to  the  latter. 

This  artifice  of  exchanging  a  measurement  of  time 
for  one  of  &pace — or  vice  versa — is  a  very  common 
one  among  astronomers.  It  was  Edmund  Halley,  the 
friend  and  pupil  of  Sir  Isaac  Newton,  who  suggested 
its  application  in  the  way  above  described.  It  will  be 
noticed  that  what  is  required  for  the  successful  appli- 
cation of  the  method  is  that  one  set  of  observers  should 
be  as  far  to  the  north  as  possible,  another  as  far  to  the 
south,  so  that  the  path  of  Yenus  may  be  shifted  as 
much  as  possible.  Clearly  the  northern  observers  will 
see  her  path  shifted  as  much  to  the  south  as  it  can  pos- 
sibly be,  while  the  southern  observers  will  see  the  path 
shifted  as  far  as  possible  toward  the  north. 

One  thing,  however,  is  to  be  remembered.  A 
transit  lasts  several  hours,  and  our  observers  must  be 
so  placed  that  the  sun  will  not  set  during  these  hours. 
This  consideration  sometimes  involves  a  difficulty. 
For  our  earth  does  not  supply  observing  room  all  over 


VENUS   ON   THE   StJN'S  FACE.  77 

her  surface,  and  the  very  region  where  observation 
would  be  most  serviceable  may  be  covered  by  a  widely- 
extended  ocean.  Then,  again,  the  observing  parties 
are  being  rapidly  swayed  round  by  the  rotating  earth ; 
and  it  is  often  difficult  to  fix  on  a  spot  which  may  not, 
through  this  cause,  be  shifted  from  a  favorable  posi- 
tion at  the  beginning  of  the  transit  to  an  unfavorable 
one  at  the  end. 

Without  entering  on  all  the  points  of  difficulty  in- 
volved by  such  considerations  as  these,  we  may  simply 
indicate  the  fact  that  the  astronomer  has  a  problem  of 
considerable  complexity  to  solve  in  applying  Halley's 
mode  of  observation  to  a  transit  of  Venus. 

It  was  long  since  pointed  out  by  the  French  as- 
tronomer Delisle  that  the  subject  may  be  attacked 
another  way — that,  in  fact,  instead  of  noticing  how 
much  longer  the  transit  lasts  in  some  places  than  in 
others,  the  astronomer  may  inquire  how  much  earlier 
it  begins  or  ends  in  some  places  than  in  others. 

Here  is  another  artifice,  extremely  simple  in  prin- 
ciple, though  not  altogether  so  simple  in  its  applica- 
tion. Our  readers  must  bear  with  us  while  we  briefly 
describe  the  qualities  of  this  second  method,  because  in 
reality  the  whole  question  of  the  transit  and  all  the 
points  which  have  to  be  attended  to  in  the  equipment 
and  placing  of  the  various  observing  parties  depend 
on  these  preliminary  matters.  Without  attending  to 
them — or  at  least  to  such  primary  points  as  we  shall 


78  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

select — it  would  be  impossible  to  form  a  clear  con- 
ception of  tlie  circumstances  with  which  astronomers 
are  about  to  deal.  There  is,  however,  no  real  diffi- 
culty about  this  part  of  the  subject,  and  we  shall  only 
ask  of  the  reader  to  give  his  attention  to  it  for  a  very 
brief  space  of  time. 

Suppose  the  whole  of  that  hemisphere  of  the  earth 
on  which  the  sun  is  shining  when  the  transit  is  about 
to  begin  were  covered  with  observers  waiting  for  the 
event.  As  Yen  us  sweeps  rapidly  onward  to  the  criti- 
cal part  of  her  path,  it  is  clear  that  some  of  these  ob- 
servers will  get  an  earlier  view  of  the  commencement 
of  the  transit  than  others  will ;  just  as  at  a  boat-race, 
persons  variously  placed  round  a  projecting  corner  of 
the  course  see  the  leading  boat  come  into  view  at 
different  times.  Some  one  observer  on  the  outer  rim 
of  the  hemisphere  would  be  absolutely  the  first  to  see 
the  transit  begin.  Then  rapidly  other  observers  would 
see  the  phenomenon  ;  and  in  the  course  of  a  few 
minutes  some  one  observer  on  the  outer  rim  of  the 
hemisphere — almost  exactly  opposite  the  first — would 
be  absolutely  the  last  to  see  the  transit  begin.  From 
that  time  the  transit  would  be  seen  by  all  for  several 
hours — we  neglect  the  earth's  rotation,  of  course — but 
the  end  of  the  transit,  like  the  beginning,  would  not 
be  seen  simultaneously  by  the  observers.  First  one 
would  see  it,  then  in  succession  the  rest,  and  last  of 
all  an  observer  almost  exactly  opposite  the  first. 


VENUS  ON  THE  SUN'S  FACE.  79 

!Now,  here  we  have  had  to  consider  four  observers 
who  occupy  exceptional  positions.  There  is  (1)  the 
observer  who  sees  the  transit  begin  earliest,  (2)  the  one 
who  sees  it  begin  latest,  (3)  the  one  who  sees  it  end 
earliest,  and  (4)  the  one  who  sees  it  end  latest.  Let 
us  consider  the  first  two  only.  Suppose  these  two 
observers  afterward  compared  notes,  and  found  out 
what  was  the  exact  difference  of  time  between  their 
respective  observations.  Is  it  not  clear  that  the  result 
would  at  once  afford  the  means  of  determining  the 
sun's  distance  ?  It  would  be  the  simplest  of  all  possi- 
ble astronomical  problems  to  determine' over  what  pro- 
portion of  her  orbit  Yenus  passed  in  the  interval  of 
time  which  elapsed  between  these  observations ;  and 
the  observers  would  now  have  learned  that  that  por- 
tion of  Yenus's  orbit  is  so  many  miles  long,  for  they 
know  what  distance  separated  them,  and  it  would  be 
easy  to  calculate  how  much  less  that  portion  of 
Yenus's  orbit  is.  Thus  they  would  learn  what  the 
length  of  her  whole  orbit  is,  thence  her  distance  from 
the  sun,  and  thence  the  sun's  distance  from  us. 

The  two  observers  who  saw  the  transit  end  earliest 
and  latest  could  do  the  like. 

Speaking  generally,  and  neglecting  all  the  com- 
plexities which  delight  the  soul  of  the  astronomer,  this 
is  Delisle's  method  of  utilizing  a  transit.  It  has  obvi- 
ously one  serious  disadvantage  as  compared  with  the 
other.  An  observer  at  one  side  of  the  earth  has  to 


80  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

bring  his  observations  into  comparison  with,  those 
made  by  an  observer  at  the  other  side  of  the  earth. 
Each  uses  the  local  time  of  the  place  at  which  he  ob- 
serves, and  it  has  been  calculated  that  for  the  result 
to  be  of  value  there  must  not  be  an  error  of  a  single 
second  in  their  estimates  of  local  time.  Now,  does  the 
reader  appreciate  the  full  force  of  this  proviso  ?  Each 
observer  must  know  so  certainly  in  what  exact  longi- 
tude he  is,  that  his  estimate  of  the  time  when  true  noon 
occurs  shall  not  be  one  second  wrong !  This  is  all 
satisfactory  enough  in  places  where  there  are  regular 
observatories.  But  matters  are  changed  when  we  are 
dealing  with  such  places  as  Woahoo,  Kerguelen  Land, 
Chatham  Island,  and  the  wilds  of  Siberia. 

Here,  however,  as  in  so  many  other  cases,  the  as- 
tronomer must  take  what  he  can  get  and  be  thankful. 
If  Nature  insists  on  not  revealing  her  secrets  unless 
astronomers  will  betake  themselves  to  all  manner  of 
desert  and  uncanny  places,  all  astronomers  can  do  is 
to  face  with  boldness  the  difficulties  thus  placed  in 
their  way,  and  to  do  their  utmost  to  bring  them  into 
complete  subjection. 

In  the  coming  transit  there  are  many  such  diffi- 
culties to  be  encountered.  In  fact,  it  is  almost  impos- 
sible to  conceive  a  transit  the  circumstances  of  which 
are  more  inconvenient.  On  the  other  hand,  however, 
the  transit  is  of  such  a  nature  that  if  once  the  prelimi- 
nary difficulties  are  overcome,  we  can  hope  more  from 


VENUS  ON  THE  SUN'S  FACE.  81 

its  indications  than  from  those  of  any  other  transit 
which  will  happen  in  the  course  of  the  next  few  cen- 
turies. 

The  transit  will  begin  earliest  for  observers  in  the 
neighborhood  of  the  Sandwich  Islands,  latest  for  ob- 
servers near  Crozet  Island,  far  to  the  southeast  of 
the  Cape  of  Good  Hope.  It  ends  earliest  for  observers 
far  to  the  southwest  of  Cape  Horn,  latest  for  observers 
in  the  northeastern  parts  of  European  Russia.  Thus 
we  see  that,  so  far  as  the  application  of  our  second 
method  is  concerned,  the  suitable  spots  are  not  situated 
in  the  most  inviting  regions  of  the  earth's  surface. 
As  the  transit  happens  on  December  8,  1874,  the 
principal  northern  stations  will  be  very  bleak  abodes 
for  the  observers.  The  southern  stations  are  in  yet 
more  dreary  regions  —  notwithstanding  the  fact  that 
the  transit  occurs  during  the  summer  of  the  southern 
hemisphere. 

For  the  application  of  Halley's  method  we  require 
stations  where  the  whole  transit  will  be  visible,  and,  as 
the  days  are  very  short  at  the  northern  stations  in 
December,  it  is  as  respects  these  that  we  encounter 
most  difficulty.  However,  it  has  been  found  that 
many  places  in  Northern  China,  Japan,  Eastern  Si- 
beria, and  Mantchooria  are  suitable  for  the  purpose. 
The  best  southern  stations  for  this  method  lie,  unfor- 
tunately, on  the  unexplored  Antarctic  Continent  and 
the  islands  adjacent  to  it ;  but  Crozet  Island,  Ker- 


82  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

guelen  Land,  and  some  other  places  more  easy  of  access 
than  the  Antarctic  Continent,  will  serve  very  well.  In- 
deed, England  has  so  many  stations  to  occupy  else- 
where that  it  is  doubtful  whether  she  will  care  to 
undertake  the  dangerous  and  difficult  task  of  exploring 
the  Antarctic  wastes  to  secure  the  best  southern  sta- 
tions. The  work  may  fairly  be  left  to  other  nations, 
and  doubtless  will  be  efficiently  carried  out. 

What  England  will  actually  undertake  has  not  yet 
been  fully  decided  upon.  "We  may  be  quite  certain 
that  she  will  send  out  a  party  to  Woahoo  or  Hawaii 
to  observe  the  accelerated  commencement  of  the  transit. 
She  will  also  send  observers  to  watch  the  retarded 
commencement,  but  whether  to  Crozet  Island,  Ker- 
guelen  Land,  Mauritius,  or  Rodriguez,  is  uncertain. 
Possibly  two  parties  will  be  sent  out  for  this  purpose, 
and  most  likely  Crozet  Island  and  Mauritius  will  be 
the  places  selected.  It  had  been  thought  until  lately 
that  the  sun  would  be  too  low  at  these  places  when  the 
transit  begins,  but  a  more  exact  calculation  of  the 
circumstances  of  the  transit  has  shown  this  to  be  a 
mistake.  Both  Crozet  Island  and  Kerguelen  Land  are 
very  likely  to  be  enveloped  in  heavy  mists  when  the 
transit  begins — that  is,  soon  after  sunrise — hence  the 
choice  of  Mauritius  or  Rodriguez  as  a  secondary 
station. 

England  will  also  be  called  on  to  take  an  important 
part  in  observing  the  accelerated  end  of  the  transit. 


VENUS  ON  THE  SUN'S  FACE.  83 

A  party  will  probably  be  sent  to  Chatham  Island  or 
Campbell  Island,  not  far  from  New  Zealand.  It  had 
been  thought  that  at  the  former  island  the  sun  would 
be  too  low ;  but  here,  again,  a  more  exact  consideration 
of  the  circumstances  of  the  transit  has  led  astronomers 
to  the  conclusion  that  the  sun  will  be  quite  high 
enough  at  this  station. 

The  Russian  observers  are  principally  concerned 
with  the  observation  of  the  retarded  end  of  the  transit, 
nearly  all  the  best  stations  lying  in  Siberia.  But 
there  are  several  stations  in  British  India  where  this 
phase  can  be  very  usefully  observed ;  and  doubtless 
the  skilful  astronomers  and  mathematicians  who  are 
taking  part  in  the  survey  of  India  will  be  invited — 
as  at  the  time  of  the  great  eclipse — to  give  their  ser- 
vices in  the  cause  of  science.  Alexandria,  also,  though 

J  J  £"} 

inferior  to  several  of  the  Indian  stations,  will  probably 
be  visited  by  an  observing  party  from  England. 

It  will  be  seen  that  England  will  thus  be  called  on 
to  supply  about  half  a  dozen  expeditions  to  view  the 
transit.  All  of  these  will  be  sent  out  in  pursuance  of 
Delisle's  mode  of  utilizing  a  transit,  so  that,  for  reasons 
already  referred  to,  it  will  be  necessary  that  they 
should  be  provided  with  instruments  of  the  utmost 
delicacy,  and  very  carefully  constructed.*  They  will 

*  It  is  held  to  be  of  the  utmost  importance  that  all  the  observing 
parties  should  use  similar  telescopes.  It  would  be  well  if  the  class  of 
telescope  selected  were  Browning's  six-inch  reflectors. 


84  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

have  to  remain  at  their  several  stations  for  a  long  time 
before  the  transit  takes  place — several  months,  at  least 
— so  that  they  may  accurately  determine  the  latitude 
of  the  temporary  observatories  they  will  erect.  This 
is  a  work  requiring  skilled  observers  and  recondite  pro- 
cesses of  calculation.  Hence  it  is  that  the  cost  of 
sending  out  these  observing  parties  is  so  considerable. 

The  only  English  party  which  will  apply  Halley's 
method  of  observation  is  the  one  which  will  be  sta- 
tioned at  Crozet  Island  or  Kerguelen  Land.  This  part 
of  their  work  will  be  comparatively  easy,  the  method 
only  requiring  that  the  duration  of  the  transit  should 
be  carefully  timed.  In  fact,  one  of  the  great  advan- 
tages of  Halley's  method  is  the  smallness  of  the  ex- 
pense it  involves.  A  party  might  land  the  day  before 
the  transit  and  sail  away  the  day  after,  with  results  at 
least  as  trustworthy  as  those  which  a  party  applying 
Delisle's  method  could  obtain  after  several  months  of 
hard  work.  It  is  to  this,  rather  than  any  other  cause, 
that  the  small  expense  of  the  observations  made  in  1769 
is  to  be  referred.  And  doubtless  had  it  been  decided 
by  our  astronomical  authorities  to  apply  Halley's 
method  solely  or  principally,  the  expense  of  the  transit- 
observations  would  have  been  materially  lessened. 
There  would,  however,  have  been  a  risk  of  failure 
through  the  occurrence  of  bad  weather  at  the  critical 
stations ;  whereas  now — as  other  nations  will  doubt- 
less avail  themselves  of  Hallev's  method — the  chance 


VENUS  ON  THE  SUN'S  FACE.  85 

that  the  transit-observations  will  fail  through  meteoro- 
logical causes  is  very  largely  diminished.  Science  will 
owe  much  to  the  generosity  of  England  in  this  respect. 

It  is,  indeed,  only  recently  that  the  possibility  of 
applying  Halley's  method  has  been  recognized.  It 
had  been  thought  that  the  method  must  fail  totally  in 
1S74.  But  on  a  more  careful  examination  of  the  cir- 
cumstances of  the  transit,  a  French  astronomer,  M. 
Puiseux,  was  enabled  to  announce  that  this  is  not  the 
case.  Almost  simultaneously  the  present  writer  pub- 
lished calculations  pointing  to  a  similar  result ;  but 
having  carried  the  processes  a  few  steps  further  than 
M.  Puiseux,  he  was  able  to  show  that  Halley's  method 
is  not  only  available  in  1874,  but  is  the  more  powerful 
method  of  the  two. 

Unfortunately,  there  is  an  element  of  doubt  in  the 
inquiry,  of  which  no  amount  of  care  on  the  part  of  our 
observers  and  mathematicians  will  enable  them  to  get 
rid.  "We  refer  to  the  behavior  of  Yenus  herself.  It 
is  to  the  peculiarity  we  are  now  to  consider  that  the 
2^<m'-failure  of  the  observations  made  in  1769  must 
be  attributed.  It  is  true  that  Mr.  Stone,  the  eminent 
first-assistant  at  the  Greenwich  Observatory,  has  man- 
aged to  remove  the  greater  part  of  the  doubts  which 
clouded  the  results  of  those  observations.  But  not 
even  his  skill  and  patience  can  serve  to  remove  the 
blot  which  a  century  of  doubt  has  seemed  to  throw 
upon  the  most  exact  of  the  sciences.  We  shall  now 


86  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

show  how  much  of  the  blame  of  that  unfortunate  cen- 
tury of  doubt  is  to  be  ascribed  to  Venus. 

At  a  transit,  astronomers  confine  their  attention  to 
one  particular  phase — the  moment,  namely,  when 
Venus  just  seems  to  lie  wholly  within  the  outline  of 
the  sun's  disk.  This  at  least  was  what  Halley  and 
Delisle  both  suggested  as  desirable.  Unfortunately, 
Yenus  had  not  been  consulted,  and  when  the  time  of 
the  transit  came  she  declined  to  enter  upon  or  leave 
the  sun's  face  in  the  manner  suggested  by  the  astrono- 
mers. Consider,  for  example,  her  conduct  when  en- 
tering on  the  sun's  face : 

At  first,  as  the  black  disk  of  the  planet  gradually 
notched  the  edge  of  the  sun's  disk,  all  seemed  going  on 
well.  But  when  somewhat  more  than  half  of  the 
planet  was  on  the  sun's  face,  it  began  to  be  noticed 
that  Yenus  was  losing  her  rotundity  of  figure.  She 
became  gradually  more  and  more  pear-shaped,  until  at 
last  she  looked  very  much  like  a  peg-top  touching  with 
its  point  the  edge  of  the  sun's  disk.  Then  suddenly — 
"  as  by  a  lightning-flash,"  said  one  observer — the  top 
lost  its  peg,  and  then  gradually  Yenus  recovered  her 
figure,  and  the  transit  proceeded  without  further 
change  on  her  part  until  the  time  came  for  her  to 
leave  the  sun's  face,  when  similar  peculiarities  took 
place  in  a  reversed  order. 

Here  was  a  serious  difficulty  indeed.  For  when 
was  the  moment  of  true  contact  ?  "Was  it  when  the 


VENUS  ON  THE   SUN'S  FACE.  87 

peg-top  figure  seemed  just  to  touch  the  edge  of  the 
sun  ?  This  seemed  unlikely,  because  a  moment  after 
the  planet  was  seen  well  removed  from  the  sun's  edge. 
"Was  it  when  the  rotund  part  of  the  planet  belonged 
to  a  figure  which  would  have  touched  the  sun's  edge 
if  the  rotundity  had  been  perfect  elsewhere  ?  This, 
again,  seemed  unlikely,  because  at  this  moment  the 
black  band  connecting  Yenus  and  the  sun  was  quite 
wide.  And,  besides,  if  this  were  the  true  moment  of 
contact,  what  eye  could  be  trusted  to  determine  the 
occurrence  of  a  relation  so  peculiar  ?  Yet  the  interval 
between  this  phase  and  the  final  or  peg-top  phase 
lasted  several  seconds — as  many  as  twenty-two  in  one 
instance  in  1769 — and  the  whole  success  of  the  obser- 
vation depended  on  exactness  within  three  or  four  sec- 
onds at  the  outside. 

"We  know  that  Yenus  will  act  in  precisely  the  same 
manner  in  1874.  If  we  had  been  induced  -to  hope  that 
improvements  in  our  telescopes  would  diminish  the 
peculiarity,  the  observations  of  the  transit  of  Mercury 
in  November,  1868,  would  have  sufficed  to  destroy  that 
hope,  for,  even  with  the  all  but  perfect  instruments  of 
the  Greenwich  Observatory,  Mercury  assumed  the  peg- 
top  disguise  in  the  most  unpleasing  manner. 

It  may  be  asked,  then,  What  do  astronomers  pro- 
pose to  do  in  1874  to  prevent  Yenus  from  misleading 
them  again  as  she  did  in  1769  ?  Much  has  already 
been  done  toward  this  end.  Mr.  Stone  undertook  a 


88  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

series  of  careful  researches  to  determine  the  law  accord- 
ing to  which  Yenus  may  be  expected  to  behave  or  to 
misbehave  herself;  and  the  result  is,  that  he  has  been 
able  to  tell  the  observers  exactly  what  they  will  have 
to  look  for,  and  exactly  what  it  is  most  important  that 
they  should  record.  In  1769,  observers  recorded  their 
observations  in  such  doubtful  terms,  owing  to  their 
ignorance  of  the  real  significance  of  the  peculiarities 
they  witnessed,  that  the  mathematicians  who  had  to 
make  use  of  those  observations  were  misled.  Hinc 
illcB  lacrymce.  Hence  it  is  that  an  undeserved  reproach 
has  fallen  upon  the  "  exact  science." 

The  amount  of  the  error  resulting  from  the  mis- 
interpretation of  the  observations  made  in  1Y69  was, 
however,  very  small  indeed,  when  its  true  character  is 
considered.  It  is,  indeed,  easy  to  make  the  error  seem 
enormous.  The  sun's  distance  came  out  some  four 
millions  of  miles  too  large,  and  that  seems  no  trifling 
error.  Then,  again,  the  resulting  estimate  of  the  dis- 
tance of  Neptune  came  out  more  than  a  hundred  mill- 
ion miles  too  great ;  while  even  this  enormous  error 
was  as  nothing  -when  compared  with  that  which  re- 
sulted when  the  distances  of  the  fixed  stars  were  con- 
sidered. 

But  this  is  an  altogether  erroneous  mode  of  esti- 
mating the  effect  of  the  error.  It  would  be  as  absurd 
to  count  up  the  number  of  hairs'  breadth  by  which  the 
geographer's  estimates  of  the  length  and  breadth  of 


VENUS  ON  THE  SUN'S  FACE.  89 

England  may  be  in  error.  In  all  such  matters  it  is 
relative  and  not  absolute  error  we  have  to  consider. 
A  microscopist  would  have  made  a  bad  mistake  who 
should  over-estimate  the  length  of  a  fly's  proboscis  by 
a  single  hair's  breadth  :  but  the  astronomer  had  made 

O  ' 

a  wonderfully  successful  measurement  of  the  sun's  dis- 
tance who  deduced  it  within  three  or  four  millions  of 
miles  of  the  true  value.  For  it  is  readily  calculable 
that  the  error  in  the  estimated  relative  bearing  of  the 
sun  as  seen  from  opposite  sides  of  the  earth  corresponds 
to  the  angle  which  a  hair's  breadth  subtends  when  seen 
from  a  distance  of  125  feet. 

The  error  was  first  detected  when  other  modes  of 
determining  the  sun's  distance  were  applied  by  the 
skilful  astronomers  and  physicists  of  our  own  day. 
We  have  no  space  to  describe  as  fully  as  they  deserve 
the  ingenious  processes  by  which  the  great  problem 
has  been  attacked  without  aid  from  Yenus.  Indeed, 
we  can  but  barely  mention  the  principles  on  which 
those  methods  depend.  But  to  the  reader  who  takes 
interest  in  astronomy,  we  can  recommend  no  subject 
as  better  worth  studying  than  the  masterly  researches 
of  Foucault,  Leverrier,  Stone,  and  Hansen,  upon  the 
problem  of  the  sun's  distance. 

The  problem  has  been  attacked  in  four  several  ways. 
First,  the  tremendous  velocity  of  light  has  been  meas- 
ured by  an  ingenious  arrangement  of  revolving  mir- 
rors ;  the  result  combined  with  the  known  time  occu- 


90  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

pied  by  light  in  travelling  across  the  earth's  orbit 
immediately  gives  the  sun's  distance.  Secondly,  a 
certain  irregularity  in  the  moon's  motion,  due  to  the 
fact  that  she  is  most  disturbed  by  the  sun  when  trav- 
ersing that  half  of  her  path  which  is  nearest  to  him, 
was  pressed  into  the  service  with  similar  results. 
Thirdly,  an  irregularity  in  the  earth's  motion,  due  to 
the  fact  that  she  circles  around  the  common  centre  of 
gravity  of  her  own  mass  and  the  moon's,  was  made  a 
means  of  attacking  the  problem.  Lastly,  Mars,  a 
planet  which,  as  we  have  already  mentioned,  approaches 
us  almost  as  nearly  as  Yenus,  was  found  an  efficient 
ally. 

The  result  of  calculations  founded  on  these  methods 
showed  that  the  sun's  distance,  instead  of  being  about 
95,000,000  miles,  is  little  more  than  91,500,000  miles. 
And  recently,  by  a  careful  reexamination  of  the  ob- 
servations made  upon  Venus  in  1769,  Mr.  Stone  has 
shown  that  they  point  to  a  similar  result. 

Doubtless,  however,  we  must  wait  for  the  transit  of 
Venus  in  1874  before  forming  a  final  decision  as  to  the 
estimate  of  the  sun's  distance  which  is  to  take  its  place 
in  popular  works  on  astronomy  during  the  next  cen- 
tury or  so.  Nothing  but  an  unlooked-for  combination 
of  unfavorable  circumstances  can  cause  the  failure  of 
our  hopes.  Certainly,  if  we  should  fail  in  obtaining 
satisfactory  results  in  1874:,  the  world  will  not  say  that 
the  generosity  of  the  English  Government  has  been  in 


RECENT  SOLAR  RESEARCHES.  91 

fault,  since  it  would  be  difficult  to  find  a  parallel  in  tlie 
history  of  modern  science  to  the  munificence  of  the 
grant  which  has  been  made  this  year  for  expeditions 
to  observe  a  phenomenon  whose  interest  and  impor- 
tance are  purely  scientific. 

(From  Si.  PauVs,  October,  1869.) 


RECENT    SOLAR    RESEARCHES. 

SINCE  the  great  eclipse  of  August,  1868,  our  knowl- 
edge respecting  the  constitution  of  the  sun  has  been 
steadily  progressing.  One  discovery  after  another  has 
been  made,  and  there  really  seems  to  be  no  reason  for 
believing  that  we  have  as  yet  nearly  reached  the  limits 
of  the  knowledge  which  spectroscopic  analysis  is  capable 
of  supplying.  Indeed,  the  invention  of  a  new  form  of 
spectroscope — the  ingenious  automatic  spectroscope  of 
Mr.  Browning — promises  soon  to  be  rewarded  by  a 
series  of  discoveries  as  important  as  any  which  have 
hitherto  been  made.  "We  propose  briefly  to  indicate 
the  present  position  of  our  knowledge  respecting  the 
great  central  luminary  of  our  system. 

The  spectroscopic  observation  of  the  eclipse  of 
August,  1868,  had  shown  that  the  strange  prominences 
seen  during  total  eclipses  of  the  sun  are  vast  masses  of 
luminous  vapor — hydrogen-flames,  we  may  call  them, 
considering  how  largely  hydrogen  enters  into  their 


92  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

constitution.  Only  we  must  remember  that  it  is  hy- 
drogen glowing  from  intensity  of  heat  simply,  and  not 
burning  hydrogen,  that  constitutes  these  prominences. 
Now,  it  had  long  been  recognized  that  the  colored 
prominences  spring  from  an  envelope  of  a  similar  na- 
ture surrounding  the  whole  surface  of  the  sun.  Father 
Secchi,  of  the  Collegio  Romano,  in  a  lecture  given  to 
the  pupils  of  the  Ecole  Ste.  Gene  vie  ve,  had  thus  in 
1867  described  this  envelope  (whose  existence  he  was 
the  first  to  recognize) :  "  The  observation  of  eclipses 
furnishes  indisputable  evidence  that  the  sun  is  really 
surrounded  by  a  layer  of  red  matter,  of  which  we  com- 
monly see  no  more  than  the  most  elevated  points." 
One  of  the  first  and  most  interesting  results  of  the 
eclipse-observations  was  Mr.  Lockyer's  confirmation  of 
the  justice  of  this  opinion.  He  and  Jannsen  had  inde- 
pendently shown  that  the  existence  of  prominences  can 
be  recognized  when  the  sun  is  not  eclipsed ;  and  the 
same  method  supplied  clear  evidence  of  the  existence 
of  this  red  envelope,  to  which  Mr.  Lockyer  gave  the 
name  of  the  chromosphere.  Remembering  who  first 
indicated  its  existence  as  "  indisputable,"  we  may  con- 
veniently call  it  Secchi's  chromosphere.  (See  note  at 
the  end  of  this  paper.) 

Both  the  chromosphere  and  the  prominences  consist 
of  glowing  vapor.  But  there  is  a  difference  in  their 
constitution.  In  the  prominences  there  are  usually  but 
very  few  constituent  vapors.  Hydrogen  is  there,  and 


RECENT   SOLAR  RESEARCHES.  93 

another  vapor,  whose  nature  is  as  yet  undetermined, 
while  occasionally  there  are  the  vapors  of  other  ele- 
ments. But  in  the  chromosphere  there  are  commonly 
several  elements,  and  sometimes  there  are  many. 

Here,  then,  we  have  above  the  photosphere  of  the 
sun  a  vaporous  envelope,  obviously  of  a  complicated 
structure,  and  perhaps  far  more  complicated  than  it  has 
yet  been  proved  to  be.  For  it  must  be  remembered 
that  the  lowest  layers  of  this  envelope  might  be  com- 
posed of  the  vapors  of  numerous  elements,  and  yet  no 
record  of  their  existence  be  recognized.  A  depth  of 
ten  miles  would  correspond  to  so  small  a  portion  of 
the  sun's  diameter  (about  the  85,000th  part)  as  to  be 
wTholly  unrecognizable  by  any  telescopic  power  men 
can  hope  to  obtain.  If  any  of  our  readers  are  telesco- 
pists,  they  will  know  what  force  lies  in  the  remark  that 
such  a  distance  would  subtend  about  the  44th  part 
of  a  second  of  arc,  so  that  no  less  than  twenty-six  such 
distances  could  be  placed  between  the  components  of 
that  well-known  test-object,  the  double  companion  of 
the  star  Gamma  Andromedoe.* 

•Next  below  this  colored  envelope  there  is  the 
mottled  photosphere,  either  a  white-hot  surface  with 

*  The  view  here  presented  was  completely  confirmed  during  the 
eclipse  of  last  December.  Professor  Young  and  Mr.  Pye  independently 
recognized  a  layer  whose  spectrum  showed  all  the  Fraunhofer  lines 
reversed.  By  observing  at  the  place  where  the  moon  had  just  concealed 
the  last  fine  sickle  of  the  solar.disk,  they  obviated  the  effects  of  diffrac- 
tion, which  render  the  observation  wholly  impossible  in  the  case  of  the 
uneclipsed  sun. 


94  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

relatively  dark  pores  all  over  it,  or,  according  to  other 
and  better  authorities,  a  surface  of  white-hot  spots 
spread  over  a  relatively  dark  background.  Here  we 
are  describing  merely  its  appearance ;  what  the  con- 
stitution of  this  surface  may  in  reality  be  remains  yet 
to  be  determined. 

Beneath  the  photosphere  there  are  vast  depths  of 
vapor,  for  when  the  photosphere  is  broken  through 
where  spots  are  formed,  the  spectroscope  tells  us  that 
the  relatively  dark  regions  thus  disclosed  are  filled 
with  the  vapors  of  various  elements.  "We  know  that 
the  dark  lines  which  cross  the  rainbow-tinted  solar 
spectrum  are  caused  by  the  light-absorbing  action  of 
the  vapors  which  surround  the  sun,  and  these  lines 
are  seen  more  distinctly  in  the  spectrum  of  a  sun-spot 
than  in  that  of  the  photosphere. 

Now,  it  is  worthy  of  notice  that  all  that  has  thus  far 
been  discovered  tends  to  confirm  the  theroy  put  for- 
ward nearly  a  century  ago  by  Sir  William  Herschel. 
That  thoughtful  observer  recognized  in  the  solar  pho- 
tosphere a  widely-extended  layer  of  luminous  clouds, 
while  he  regarded  the  light  of  the  penumbrse  of  sun- 
spots  as  coming  from  a  lower  cloud-layer.  He  con- 
ceived that  up-rushes  of  vapor,  thrusting  aside  both 
layers,  caused  the  appearance  of  a  solar  spot.  We  have 
heard  a  great  deal  lately  of  the  English  and  Conti- 
nental theories  of  the  solar  •constitution ;  but  the 
evidence  we  have  recently  obtained  goes  far  to  show 


RECENT  SOLAR  RESEARCHES.  95 

that,  after  all,  Sir  William  Herscliel,  without  the  aid 
of  spectroscope  or  polariscope,  formed  a  juster  view  of 
the  solar  constitution  than  any  which  has  been  recently 
propounded.  He  was  doubtless  mistaken  in  the  view 
(which  he  put  forward  as  a  mere  hypothesis)  that  the 
real  surface  of  the  sun  may  be  not  very  intensely 
heated.  We  have  every  reason  to  believe  that  the 
whole  mass  of  the  sun  is  raised  to  an  inconceivable 
degree  of  heat.  But  for  the  rest,  there  seems  far  more 
reason  to  believe  in  Sir  William  Herschel's  cloud- 
layer  theory  than  in  any  other  which  has  been  put 
forward  in  recent  times. 

Let  us  consider  some  of  the  consequences  of  such  a 
constitution.  Imagine  the  ascent  of  vapors  of  many 
elements  from  the  fluid  surface  of  the  solar  oceans. 
This  mixed  atmosphere  is  in  reality  aglow  with  the 
intensest  heat  and  light,  so  that,  if  we  could  examine 
its  spectrum  separately,  we  should  see  the  bright  lines 
*of  the  various  vaporous  elements  which  constitute  it. 
But  intensely  hot  as  it  is,  it  must  yet  be  less  hot  than 
the  surface  from  which  it  has  risen,  because  the  forma- 
tion of  vapors  is  a  process  in  which  heat  is  used  up. 
And  therefore,  by  a  well-known  law,  the  spectrum  of 
the  light  from  the  white-hot  surface  shining  througli 
the  atmosphere  will  be  a  rainbow-tinted  streak,  crossed 
by  the  dark  lines  corresponding  to  the  various  elements 
composing  that  atmosphere.  But  as  the  lighter  vapors 
in  this  mixed  atmosphere  ascend,  they  reach  a  region 


96  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

of  less  pressure,  and  a  region  where  they  can  part  more 
freely  with  their  heat.  Thus,  precisely  as  the  cumulus- 
clouds  form  in  our  own  atmosphere,  so  would  a  layer 
of  clouds  be  formed  somewhat  low  down  in  the  solar 
atmosphere.  But  from  the  upper  surface  of  this  layer 
the  vapors  of  the  elements  composing  the  clouds  would 
rise,  again  to  condense  at  a  higher  level,  much  as  the 
light  cirrus-clouds  in  our  own  atmosphere  form  at  a 
great  height  above  the  layer  of  cumulus-clouds. 

The  great  difference  between  this  process  and  what 
takes  place  in  our  own  atmosphere  would  consist  in 
the  fact  that  whereas  the  only  kind  of  cloud  which  can 
form  in  our  air  is  a  water-cloud,  there  can  be  formed  in 
the  solar  atmosphere  clouds  of  iron,  copper,  zinc,  and 
other  such  elements,  each  element  having  its  own 
distinct  range,  so  to  speak,  within  the  limits  of  the 
solar  atmosphere. 

Now,  with  such  processes  as  these  going  on,  we  can 
conceive  how  rushes  of  heated  gas  might  from  time  to' 
time  thrust  aside  the  cloud-layers  ;  and  how  where  this 
happened  we  should  occasionally  recognize  the  bright 
lines  corresponding  to  the  more  intensely-heated  gas, 
as  well  as  the  dark  lines  corresponding  to  the  deep 
vapor-masses  laid  bare  by  the  removal  of  the  photo- 
sphere. And  precisely  in  this  way  do  the  observations 
recently  made  by  Mr.  Lockyer  seem  alone  to  be  expli- 
cable. He  sees  the  glowing  vapors  above  the  photo- 
sphere stirred  from  time  to  time  as  by  fierce  tempests — 


RECENT  SOLAR  RESEARCHES.  97 

nay,  lie  is  enabled  to  measure  (very  roughly,  of  course) 
the  velocity  with  which  these  solar  winds  urge  their 
way  through  the  chromosphere  itself,  in  the  neighbor- 
hood of  these  spots.  The  progress  of  these  hurricanes 
is  often  indicated  by  the  appearance  of  bright  lines  in 
those  parts  of  the  spectrum  where  usually  dark  lines 
are  seen. 

Truly  KirchhofPs  discovery  of  the  significance  of  the 
spectral  lines  is  bearing  wonderful  fruit !  Who  would 
have  thought  that  researches  carried  on  with  a  few 
triangular  prisms  of  glass  on  the  light  from  such  a 
substance  as  sodium,  the  basis  of  our  commonplace 
soda,  would  lead  to  the  result  that  solar  tornadoes 
could  be  watched  as  readily  with  the  spectroscope  as 
in  Galileo's  time  the  sun-spots  themselves  could  be 
traced  across  the  sun's  disk  with  the  telescope  ?  * 

(From  the  Spectator  for  July  2,  1870.) 

*  I  give  this  paper  as  it  appeared  in  the  Spectator.  But  there  are 
some  points  requiring  correction.  In  the  first  place,  the  objectionable 
word  chromosphere  (for  chromatosphere)  should  be  replaced  by  sierra. 
Secondly,  there  is  an  error  as  to  the  absolute  priority  of  Secchi  in  recog- 
nizing the  sierra.  He  went  considerably  beyond  all  others  in  the  matter, 
having  not  only  reasoned  upon,  but  seen  and  photographed  the  sierra, 
and  having  furthermore  found  evidence  as  to  its  nature  when  studying 
sun-spots.  But  Professors  Grant  and  Swan,  as  well  as  Von  Littrow,  the 
Imperial  Astronomer  of  Austria,  had  recognized  the  existence  of  the 
sierra  before  Secchi,  and  Leverrier  had  also  independently  arrived  at  the 
same  conclusion  as  Secchi,  and  at  about  the  same  time.  I  had  not  known 
of  some  of  these  claims  and  had  forgotten  others  when  I  wrote  the  above 
paper.  This  will  scarcely  seem  surprising  when  it  is  remembered  that 
the  views  of  Grant,  Swan,  Yon  Littrow,  and  Leverrier,  had  not  been  made 
widely  public — as  Secchi's  had — by  being  published  in  popular  treatises 


98  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 


GOVERNMENT  AID  TO  SCIENCE. 

AMONG  the  questions  which  will  occupy  the  atten- 
tion of  the  new  Parliament,  we  think  we  may  safely 
include,  in  anticipation,  the  subject  of  State  inter- 
vention to  secure  the  progress  of  physical  science.*  It 
will  be  remembered  that  this  subject  was  brought  be- 
fore the  notice  of  the  British  Association,  at  its  recent 
meeting,  by  Lieutenant-Colonel  Strange,  and  a  com- 
mittee— including  the  names  of  Professors  Sir  "William 
Thomson,  Tyndall,  Frankland,  "Williamson,"  Stokes, 
Fleming,  Jenkins,  Hirst,  and  Huxley,  Messrs.  Glaisher 
and  Huggins,  and  Drs.  Stenhouse,  Balfour  Stewart, 
and  Mann — was  appointed  to  consider  and  report  upon 
the  subject.  Science  has  now  reached  a  peculiar  stage 

and  in  lectures.  It  was  with  some  surprise,  therefore,  that  I  found  my- 
self charged,  not  only  with  ignorance,  but,  incongruously  enough,  with 
injustice  also,  by  a  fellow-worker  in  astronomy,  who  addressed  a  letter 
to  the  editor  of  the  Spectator,  advocating  in  needlessly  warm  terms  the 
prior  claims  of  Grant  and  Swan.  It  is  perhaps  unnecessary  for  me  to 
say  that  the  charge  of  injustice  was  wholly  undeserved ;  and  I  think  the 
writer  of  the  letter  would  have  inferred  this  had  he  considerred  a  parallel 
instance  which  had  recently  occurred.  For  a  well-known  worker  had 
claimed  the  very  same  discovery  only  a  few  months  before  as  kis  own  ; 
and,  although  the  subject  was  specially  his,  he  had  not  known  even  of 
Secchi's  numwbus  public  statements  respecting  the  sierra,  yet  no  one 
thought  of  charging  him  with  injustice.  The  writer  of  the  letter  could 
scarcely  have  forgotten  the  circumstance,  since  that  worker  was  no  other 
than  himself. 

*  The  reader  need  hardly  be  told  that  the  hopes  here  expressed  were 
completely  disappointed. 


GOVERNMENT  AID  TO  SCIENCE.  99 

in  that  long  and  remarkable  career  of  progress  which 
was  inaugurated  toward  the  close  of  the  sixteenth 
century.  Hitherto  those  who  have  been  able  and  will- 
ing to  take  part  in  scientific  researches  have  had  the 
means  of  doing  so  without  incurring  great  expense, 
and  many  have  even  found  it  possible  to  do  good  and 
useful  service  in  the  cause  of  science  while  prosecuting, 
at  the  same  time,  the  labors  of  their  profession  or  trade. 
But  now  the  case  is  very  different.  A  man  who  would 
assist  in  forwarding  the  progress  of  science  must  give 
his  whole  energies  to  the  cause ;  he  must  be  prepared 
to  incur  large  expenses ;  and  all  this  he  must  do  with- 
out the  hope  that  science  will  make  him  any  pecuniary 
return.  Theoretically,  indeed,  it  may  bo  argued  that 
he  will  labor  best  who  hopes  for  no  return  for  his 
labors ;  who  works,  not  for  profit,  but  from  pure  love 
of  science,  and  so  on.  But,  as  a  matter  of  fact,  many 
of  those  who  would  serve  science  best,  and  hundreds 
of  those  who  could  do  yeoman's  service  in  her  cause, 
are  simply  debarred  from  scientific  pursuits  by  the 
necessity  of  earning  the  means  of  subsistence.  And 
there  are  crowds  of  others  who,  though  they  may  be 
independent  in  means,  are  yet  unable  to  provide  them- 
selves with  the  expensive  instruments  by  which  alone 
any  useful  work  can  now  be  done.  For,  as  Colonel 
Strange  observes,  "  Science  can  no  longer  be  cultivated 
as  in  by-gone  times  it  used  to  be.  In  astronomy  the 
man  with  his  table  spy-glass  cannot  now  furnish  ac- 


100  LIGHT   SCIENCE  FOR  LEISURE  HOURS. 

eeptable  results.  In  chemistry,  the  Wollaston  tea-tray 
and  wine-glasses  are  superseded  by  well-equipped  lab- 
oratories. In  optics  we  see  elaborate  spectroscopes, 
not  Newton's  simple  prism.  In  meteorology,  and  in 
every  investigation  of  continuous  phenomena,  we  are 
satisfied  with  nothing  less  than  self-recording  instru- 
ments. In  electricity,  in  microscopy,  and  in  other 
branches,  our  appliances  are  every  day  more  and  more 
amplified.  The  age  of  great  discoveries  made,  and, 
above  all,  extensive  series  of  facts  accumulated  with 
limited  means,  is  passing  away  ;  and  we  are  every  day 
compelled  to  employ  more  perfect  appliances  and  more 
systematic  agencies  in  unravelling  the  secrets  of  Na- 
ture." 

It  is  scarcely  necessary  to  point  out  that  the  aid  of 
the  State  in  securing  the  progress  of  physical  science 
is  not  asked  without  the  promise  of  a  quid  pro  quo.  It 
is  not  as  though  the  State  were  called  upon  to  aid  in 
antiquarian,  or  entomological,  or  numismatic  researches, 
or  in  any  subject  of  inquiry  which,  however  interesting, 
has  no  practical  bearing  on  the  wants  of  daily  life,  or 
on  the  appliances  by  which  the  social  state  of  man  may 
be  benefited  and  improved.  Nor  is  it  to  secure  the 
spread  of  .scientific  knowledge  that  State  aid  is  called 
for,  but  to  secure  the  progress  of  physical  science. 
That  that  progress  cannot  fail  to  bring  with  it  im- 
portant advantages  to  mankind  it  is  almost  needless  to 
assert.  We  have  only  to  look  around  us  to  see  what 


GOVERNMENT  AID   TO  SCIENCE.  101 

science  lias  doire  for  mankind.  But  those  are  best 
acquainted  with  the  practical  vaiuje, of  s>;ientifi'& knowl- 
edge who  are  themselves  /engaged  ]  r,n§  tgdip^ijfes  re- 
searches, or  are  at  least  proficient  in  scientific  "matters. 
Hundreds,  for  example,  might  see  in  the  complicated 
instruments  which  are  to  be  found  in  the  Greenwich 
Observatory  nothing  but  ingenious  applications  for  the 
solution  of  theoretical  problems ;  it  is  only  astronomers, 
or  those  who  are  versed  in  the  processes  of  astronomy, 
who  know  that  our  whole  system  of  commerce  would 
be  affected  injuriously  if  those  instruments  were  de- 
stroyed or  left  unused.  Here  we  have  an  instance  of 
science  working  under  State  patronage,  working  in  the 
cause  of  the- State;  and  what  Colonel  Strange  proposes 
is  to  multiply  instances  of  this  sort.  The  State  profits 
by  the  labors  of  the  Greenwich  astronomers,  and  those 
astronomers  would  for  the  most  part  be  unable  or  un- 
willing to  continue  their  labors  but  for  the  pecuniary 
reward  which  they  receive  from  the  State.  But  as- 
suredly the  State  would  suffer  more  than  the  astrono- 
mers if  the  establishment  at  Greenwich  were  done 
away  with.  And  precisely  in  the  same  way  the  State 
would  reap  important  advantages  from  the  labors  of 
proficients  in  other  departments  of  science  who  are 
now  debarred  by  considerations  of  expense,  or  by  the 
necessity  of  earning  a  livelihood,  from  applying  their 
skill  to  forward  the  cause  of  scientific  progress. 

Colonel  Strange's  proposal  includes  the  establish- 


102  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

ment  of  national  institutions  expresslyfor  the  practical 
advancement  of  scientific  research.  He  remarks  that 
",mert  engaged; in  ^denee.  need  hardly  be  told  that 
when  they  discover  a  new  substance,  the  determination 
of  the  physical  properties  of  which  is  attended  with 
cost  and  labor,  they  experience  a  great — perhaps 
insuperable — difficulty  in  obtaining  its  examination. 
A  new  theory,  or  the  confutation  or  continuation  of  an 
old  one,  if  dependent  on  any  considerable  accumulation 
of  facts,  shares  even  a  worse  fate."  Important  benefits 
could  not  fail  to  result  if  difficulties  such  as  these 
were  removed  from  the  paths  of  physical  research,  by 
the  institution  of  bodies  whose  duty  it  would  be  to 
undertake,  and  complete  in  an  accurate  and  systematic 
manner,  costly  and  tedious  investigations  on  which 
vast  interests  may  be  dependent. 

(From  the  Daily  News  for  December  9,  1869.) 


AMERICAN  ALMS  FOR  BRITISH  SCIENCE* 

OUR  astronomers  have  received  an  invitation  which 
is  as  pleasing  to  them  as  men  of  science  as  it  is  painful 

*  This  was  one  of  a  series  of  articles  which  appeared  in  the  Daily 
News  during  the  months  which  followed  the  announcement  that  the 
British  Government  would  give  no  aid  to  the  eclipse  expedition.  To  the 
liberality  with  which  the  Daily  News  gave  space  for  these  appeals  may 
fairly  be  ascribed  the  fact  that  eventually  the  eclipse  committee  was 
aroused  to  something  like  energetic  action.  When  the  real  state  of  the 
case  became  known  to  Government,  ample  assistance  was  rendered.  The 


AMERICAN  ALMS  FOR  BRITISH  SCIENCE.  103 

to  them  as  Englishmen.  As  our  readers  know,  sixty- 
eight  persons  had  volunteered  to  go  to  Spain  and  Sicily 
to  view  the  total  eclipse  of  December  22d ;  our  scientific 
societies  had  voted  large  sums  of  money  for  the  equip- 
ment of  the  two  observing  parties ;  and  every  one  was 
certain  that  Government  would  supply  the  means  of 
transport.  But  every  one  was  mistaken.  The  Ad- 
miralty discovered  that  the  nation  would  assuredly 
disapprove  if  room  were  found  for  mere  men  of  science 
and  their  trumpery  in  any  of  her  Majesty's  ships ;  and 
accordingly,  just  when  the  extensive  preparations  re- 
quisite for  the  expeditions  were  in  full  progress,  news 
came  that  the  means  of  transport  must  be  found  by 
the  observers  themselves.  "We  do  not  care  here — we 
hardly  have  patience,  indeed — to  discuss  the  probable 
cause  of  a  refusal  so  discreditable  to  the  scientific 
repute  of  England.  It  had  been  announced  by  the 
Astronomer-Royal  (in  connection  with  another  matter), 
that  Government  would  always  be  found  liberal  in 
scientific  matters,  if  a  sufficient  cause  were  shown  by 
persons  in  whom  they  had  trust ;  and  we  do  not  care 
to  inquire  whether  the  Astronomer-Eoyal  was  mistaken 
in  this  matter,  or  whether  the  Government  declined  to 

shortness  of  the  time  eventually  left  for  preparation  may  be  regarded  as 
accounting  for  subsequent  seeming  short-comings  on  the  part  of  the 
Organizing  Committee ;  while  fortunately  the  zeal  of  the  expeditionists 
averted  the  risk  (which  at  one  time  seemed  serious)  that  rather  brusque 
usage  would  cause  some  of  the  most  important  members  of  the  expedi- 
tions to  withdraw  their  aid. 


104  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

put  trust  in  him  or  in  the  Presidents  of  our  Astro- 
nomical and  Royal  Societies,  or  whether,  lastly,  the 
sufficient  cause  was  not  brought  before  the  Govern- 
ment with  proper  earnestness.  Let  the  explanation  be 
what  it  may,  the  fact  remains — England  lias  been 
exhibited  to  all  the  nations  as  turning  her  back  on 
science,  and  English  men  of  science  have  been  dis- 
credited before  the  world  as  unworthy  of  England's 
confidence. 

But  now  news  comes  that  the  Government  of  the 
United  States  has  not  only  found  means  of  transport 
for  two  American  parties,  but  has  made  the  handsome 
grant  of  £6,000,  to  furnish  suitable  appliances  for  ob- 
serving the  eclipse.  The  American  men  of  science 
have  reached  England.  They  recognize  the  pitiable 
condition  to  which  our  astronomers  have  been  reduced 
by  the  Government,  and  they  invite  our  sixty-eight 
volunteers  to  sail  with  them.  A  letter  has  been  sent 
to  these  volunteers,  inviting  them,  in  the  name  of  the 
American  expeditionary  parties,  to  accept  this  much- 
needed  assistance.  The  offer  is  most  generous ;  it  is 
most  inviting ;  it  is  one  which  no  astronomer  is  justi- 
fied in  declining  on  account  of  sentimental  considera- 
tions. But  it  certainly  is  a  new  and  a  painful  position 
for  an  English  man  of  science  to  be  placed  in,  thus  to 
find  scientific  alms  offered  him  as  a  reparation  for  the 
insult  he  has,  in  effect,  received  from  his  own  Govern- 
ment. 


AMERICAN  ALMS  FOR  BRITISH  SCIENCE.  105 

Many  may  be  disposed  to  wonder  why  so  mucli  in- 
terest is  attached  to  this  particular  eclipse.  During 
many  former  total  eclipses — even  when  they  have  been 
visible  at  more  conveniently  accessible  stations — less 
care  was  taken  to  fit  out  expeditions.  And,  what  is 
even  more  to  the  point,  observations  have  been  made 
on  eclipse  after  eclipse,  in  former  times,  without  add- 
ing jot  or  tittle  to  our  knowledge  of  solar  physics.  But 
during  recent  eclipses  things  have  altered.  In  1860 
the  celebrated  "  Himalaya  Expedition  "  sailed  to  Spain 
from  England ;  while  other  parties  came  from  France, 
Italy,  and  Germany.  And,  though  the  old  fault  of 
wasting  observing  energy  on  matters  already  known 
or  demonstrated  prevailed  very  largely,  yet  De  la  Eue 
and  Secchi,  by  photographing  the  eclipsed  sun,  well 
repaid  the  whole  cost  of  these  expeditions.  In  the 
great  total  eclipse  of  August,  1868,  Europe  sent  out 
many  observing  parties  to  India,  and  the  great  dis- 
covery that  the  red  prominences  seen  round  the  totally- 
eclipsed  sun  are  masses  of  glowing  vapor  sufficiently 
repaid  the  cost.  In  August,  1869,  the  Americans 
availed  themselves  right  skilfully  and  worthily  of  the 
passage  of  the  moon's  shadow  across  their  continent ; 
and,  though  they  failed  in  the  main  purpose  they  had 
set  themselves,  they  made  preliminary  observations  of 
the  utmost  importance  and  value.  That  purpose  was 
to  ascertain  the  nature  of  the  glorious  aureole  of  light 
Been  around  the  sun  during  total  eclipses ;  and  it  is 


106  LIGHT  SCIEXCE  FOR  LEISURE  HOURS. 

with  the  same  purpose  that  the  expeditions  formed  for 
observing  the  present  eclipse  were  to  have  set  forth. 
The  questions  to  be  answered  are  full  of  interest,  even 
now  when  their  full  significance  is  not  known ;  while 
it  may  well  be  that  when  we  begin  to  have  accurate 
information  about  them,  we  shall  find  they  have  a  real 
importance  wholly  unlocked  for.  As  the  last  direct 
rays  of  the  sun  are  concealed  by  the  advancing  moon, 
there  springs  into  view  a  glorious  crown  of  colored 
light — pearly  wrhite  in  parts,  faintly  pink  beyond,  and 
at  the  extreme  verge  showing  tints  of  mauve  and 
violet  and  green — delicate  and  beautiful  beyond  de- 
scription. Through  this  coronal  glory  there  extend 
rays  of  bluish-white  light,  reaching  often  to  a  vast  dis- 
tance from  the  black  disk  of  the  moon.  Commonly 
remaining  unchanged  in  position,  these  rays  sometimes 
— if  all  the  narratives  can  be  trusted — exhibit  very 
obvious  signs  of  motion,  resembling  in  this  respect 
those  streamers  of  colored  light  which  we  have  lately 
so  much  admired  in  the  aurora.  Indeed,  wonderful  as 
it  may  seem,  the  corona  has  lately  come  to  be  regarded 
as  associated  in  some  way  with  the  Aurora  Borealis. 
"We  know  that  those  auroral  streamers  which  form  so 
wonderful  a  display  in  our  own  skies  are  due  to  solar 
influences.  In  whatever  way  it  may  be  brought  about, 
certain  it  is  that  disturbances  of  the  sun  are  reflected 
in  terrestrial  auroral  displays.  The  auroras  which 
have  occurred  lately  were  predicted  by  astronomers, 


AMERICAN  ALMS  FOR  BRITISH  SCIENCE.  107 

wlio  know  tliat  tlie  sun  is  undergoing  during  the 
present  year  disturbances  of  the  most  amazing  nature. 
Solar  spots,  of  various  dimensions,  have  been  counted 
by  the  hundred  of  late  ;  and  we  now  know  that  when 
the  sun  is  thus  spotted  our  earth  sympathizes  with  the 
central  orb.  Thrilling  from  pole  to  pole  in  magnetic 
tremor,  she  spreads  out  over  both  hemispheres  the 
auroral  banners  that  indicate  the  progress  of  electric 
revolutions.  The  devices  of  her  children  for  utilizing 
her  electric  forces  are  for  the  time  set  at  naught,  and 
the  telegraph-clerk  finds  for  a  while  that  Mother 
Earth  is  having  her  own  way  and  will  not  obey  his  be- 
hests. If  the  sun,  ninety  millions  of  miles  away  from 
us,  thus  affects  the  earth's  frame,  and  thus  illuminates 
terrestrial  skies,  it  need  not  be  greatly  wondered  at 
should  it  be  proved  that  he  illuminates  with  no  dis- 
similar light  the  regions  lying  more  closely  around 
him.  If  there  are  no  planets  like  our  earth  in  these 
regions,  no  large  bodies  on  which  the  sun  can  exert 
his  inconceivable  powers,  there  are  yet  in  these  spaces 
— unless  astronomers  are  at  fault — uncounted  millions 
of  minute  bodies,  those  tiny  "  pocket-planets  "  which 
pass  at  times  through  our  own  atmosphere,  and  are 
called  by  us  falling  stars,  or  meteors.  Among  these 
tiny  bodies  auroral  gleams  may  pass,  producing  by 
their  united  lustre  the  glories  of  the  solar  corona. 

But,  whether  this  view  be  just,  or  whether,  as  Mr, 
Lockyer  holds,  the  corona  is  only  a  phenomenon  of 


108  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

our  own  air,  or  is  due  (as  the  fanciful  M.  Faye  once 
thought  of  the  colored  prominences)  to  some  sort  of 
lunar  mirage,  certain  it  is  that  just  now  it  is  a  matter 
of  extreme  interest  that  further  observations  should  be 
made.  Undoubtedly,  what  we  have  lately  learned  re- 
specting the  sun  gives  an  interest  and  importance  to 
this  matter  of  the  solar  corona  which  it  never  before 
possessed.  Yet  this  is  the  problem  respecting  which 
our  Government  is  understood  to  have  said  to  astron- 
omers, "  As  far  as  we  can,  we  will  prevent  you  from 
solving  it." 

Truly  it  would  be  difficult  to  show  that  any  ma- 
terial profit  can  be  gained  by  solving  the  problems 
associated  with  the  solar  corona.  The  tree  of  science 
has  its  blossoms  as  well  as  its  fruits,  and  perhaps  the 
results  of  the  observations  we  are  advocating  will  be- 
long to  the  former  rather  than  the  latter.  But  what 
then  ?  Can  we  limit  science  to  remunerative  researches 
alone?  As  well  might  we  attempt  to  get  fruit  from 
a  tree  whose  leaves  and  blossoms  we  systematically 
plucked  off.  Latent  though  the  power  of  science  now 
is  in  great  part,  yet  science  is  the  greatest  power  our 
country  possesses.  It  has  been  treated  for  a  long 
while  as  a  troublesome  beggar — a  few  hundreds  doled 
out  here  and  a  few  thousands  there.  The  country  does 
not  yet  know  its  own  interest.  Because  little  has  been 
asked,  it  has  thought  little  could  be  returned.  The 
time  is  coming  when  not  hundreds  or  thousands  will 


THE  SECRET  OF  THE  NORTH  POLE.  109 

be  asked  for  science,  but  millions  freely  and  eagerly 
given — when  the  example  of  other  countries,  rapidly 
passing  in  advance  of  England  through  their  scientific 
resources,  will  force  on  our  attention  the  folly  of  a  sys- 
tem which  grants  thirty  millions  yearly  to  secure  the 
means  of  carrying  on  war,  and  refuses  a  few  paltry 
thousands  to  secure  the  noblest  portion  of  our  strength. 

(From  the  Daily  News  for  November  5,  1870.) 


THE  SECRET  OF  THE  NORTH  POLE. 

IF  an  astronomer  upon  some  distant  planet  has  ever 
thought  the  tiny  orb  we  inhabit  worthy  of  telescopic 
study,  there  can  be  little  doubt  that  the  snowy  regions 
which  surround  the  arctic  and  antarctic  poles  must 
have  attracted  a  large  share  of  his  attention.  "Waxing 
and  waning  with  the  passing  seasons,  those  two  white 
patches  afford  significant  intelligence  respecting  the 
circumstances  of  our  planet's  constitution.  They  mark 
the  direction  of  the  imaginary  axial  line  upon  which 
the  planet  rotates;  so  that  we  can  imagine  how  an 
astronomer  on  Mars  or  Yenus  would  judge  from  their 
position  how  it  fares  with  terrestrial  creatures.  There 
may,  indeed,  be  Martial  Wheweils  who  laugh  to  scorn 
the  notion  that  a  globe  so  inconveniently  circumstanced 
as  ours  can  be  inhabited,  and  are  ready  to  show  that  if 
there  were  living  beings  here  they  must  be  quickly 


110  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

destroyed  by  excessive  heat.  On  the  other  hand,  there 
are  doubtless  skeptics  on  Yenus  also  who  smile  at  the 
vanity  of  those  who  can  conceive  a  frozen  world,  such 
as  this  our  outer  planet,  to  be  inhabited  by  any  sort 
of  living  creature.  But  we  doubt  not  that  the  more 
advanced  thinkers  both  in  Mars  and  Yenus  are  ready 
to  admit  that,  though  we  must  necessarily  be  far  infe- 
rior beings  to  themselves,  we  yet  manage  to  "  live  and 
move  and  have  our  being  "  on  this  ill-conditioned  globe 
of  ours.  And  these,  observing  the  earth's  polar  snow- 
caps,  must  be  led  to  several  important  conclusions 
respecting  physical  relations  here. 

It  is,  indeed,  rather  a  singular  fact  to  contemplate, 
that  ex-terrestrial  observers,  such  as  these,  may  know 
much  more  than  we  ourselves  do  respecting  those  mys- 
terious regions  which  lie  close  around  the  two  poles. 
Their  eyes  may  have  rested  on  spots  which  with  all  our 
endeavors  we  have  hitherto  failed  to  reach.  Whether, 
as  some  have  thought,  the  arctic  pole  is  in  summer 
surrounded  by  a  wide  and  tide-swayed  ocean ;  whether 
there  lies  around  the  antarctic  pole  a  wide  continent 
bespread  with  volcanic  mountains  larger  and  more 
energetic  than  the  two  burning  cones  which  Ross  found 
on  the  outskirts  of  this  desolate  region ;  or  whether  the 
habitudes  prevailing  near  either  pole  are  wholly  differ- 
ent from  those  suggested  by  geographers  and  voyagers 
— such  questions  as  these  might  possibly  be  resolved 
at  once,  could  our  astronomers  take  their  stand  on 


THE  SECRET  OF  THE  NORTH  POLE.  m 

some  neighboring  planet,  and  direct  the  searching 
power  of  their  telescopes  upon  this  terrestrial  orb. 
For  this  is  one  of  those  cases  referred  to  by  Humboldt, 
when  he  said  that  there  are  circumstances  under  which 
man  is  able  to  learn  more  respecting  objects  millions 
of  miles  away  from  him  than  respecting  the  very  globe 
which  he  inhabits. 

If  we  take  a  terrestrial  globe,  and  examine  the 
actual  region  near  the  North  Pole  which  has  as  yet 
remained  un visited  by  man,  it  will  be  found  to  be  far 
smaller  than  most  people  are  in  the  habit  of  imagining. 
In  nearly  all  maps  the  requirements  of  charting  result 
in  a  considerable  exaggeration  of  the  polar  regions. 
This  is  the  case  in  the  ordinary  "  maps  of  the  two 
hemispheres  "  which  are  to  be  found  in  all  atlases. 
And  it  is,  of  course,  the  case  to  a  much  more  remark- 
able extent  in  what  is  termed  Mercator's  projection. 
In  a  Mercator's  chart  we  see  Greenland,  for  example, 
exaggerated  into  a  continent  fully  as  large  as  South 
America,  or  to  seven  or  eight  times  its  real  dimen- 
sions. 

There  are  three  principal  directions  in  which  ex- 
plorers have  attempted  to  approach  the  North  Pole. 
The  first  is  that  by  way  of  the  sea  which  lies  between 
Greenland  and  Spitzbergen.  We  include  under  this 
head  Sir  Edward  Parry's  attempt  to  reach  the  pole  by 
crossing  the  ice-fields  which  lie  to  the  north  of  Spitz- 
bergen. The  second  is  that  by  way  of  the  straits 


112  LIGHT  SCIENCE   FOR  LEISURE  HOURS. 

which  lie  to  the  west  of  Greenland.  The  third  is  that 
pursued  by  Russian  explorers  who  have  attempted  to 
cross  the  frozen  seas  which  surround  the  northern 
shores  of  Siberia. 

In  considering  the  limits  of  the  unknown  north- 
polar  regions,  we  shall  also  have  to  take  into  account 
the  voyages  which  have  been  made  around  the  northern 
shores  of  the  American  Continent  in  the  search  for  a 
"  northwestern  passage."  The  explorers  who  set  out 
upon  this  search  found  themselves  gradually  forced  to 
seek  higher  and  higher  latitudes  if  they  would  find  a 
wray  round  the  complicated  barriers  presented  by  the 
ice-bound  straits  and  islands  which  lie  to  the  north  of 
the  American  Continent.  And  it  may  be  noticed  in 
passing,  as  a  remarkable  and  unforeseen  circumstance, 
that  the  farther  north  the  voyagers  went  the  less  severe 
was  the  cold  they  had  to  encounter.  "We  shall  see  that 
this  circumstance  has  an  important  bearing  on  the  con- 
siderations we  shall  presently  have  to  deal  with. 

One  other  circumstance  respecting  the  search  for 
the  northwest  passage,  though  not  connected  very 
closely  with  our  subject,  is  so  singular  and  so  little 
known  that  we  feel  tempted  to  make  mention  of  it  at 
this  point.  The  notion  with  which  the  seekers  after  a 
northwest  passage  set  out  was  simply  this,  that  the 
easiest  way  of  reaching  China  and  the  East  Indies  was 
to  pursue  a  course  resembling  as  nearly  as  possible  that 
on  which  Columbus  had  set  out — if  only  it  should 


THE  SECRET   OF  THE  NORTH  POLE.  H3 

appear  tliat  no  impassable  barriers  rendered  such  a 
course  impracticable.  They  quickly  found  that  the 
American  Continents  present  an  unbroken  line  of  land 
from  high  northern  latitudes  far  away  toward  the  ant- 
arctic seas.  But  it  is  a  circumstance  worth  noticing, 
that  if  the  American  Continents  had  no  existence,  the 
direct  westerly  course  pursued  by  Columbus  was  not 
only  not  the  nearest  way  to  the  East-Indian  Archi- 
pelago, but  was  one  of  the  longest  routes  which  could 
possibly  have  been  selected.  Surprising  as  it  may  seem 
at  first  sight,  a  voyager  from  Spain  for  China  and  the 
East  Indies  ought,  if  he  sought  the  absolutely  shortest 
path,  to  set  out  on  an  almost  direct  northerly  route ! 
He  would  pass  close  by  Ireland  and  Iceland,  and  so, 
near  the  North  Pole,  and  onward  into  the  Pacific. 
This  is  what  is  called  the  great-circle  route  ;  and  if  it 
were  only  a  practicable  one,  would  shorten  the  course 
to  China  by  many  hundreds  of  miles. 

Let  us  return,  however,  to  the  consideration  of  the 
information  which  arctic  voyagers  have  brought  us  con- 
cerning the  north-polar  regions. 

The  most  laborious  researches  in  arctic  seas  are 
those  which  have  been  carried  out  by  the  searchers 
after  a  northwest  passage.  We  will  therefore  first  con- 
sider the  limits  of  the  unknown  region  in  this  direction. 
Afterward  we  can  examine  the  results  of  those  voy- 
ages which  have  been  undertaken  with  the  express 
purpose  of  reaching  the  North  Pole  along  the  three 
principal  routes  already  mentioned. 


114  LIGUT  SCIENCE  FOR  LEISURE  HOURS. 

If  we  examine  a  map  of  North  America  constructed 
in  recent  times,  we  shall  find  that  between  Greenland 
and  Canada  an  immense  extent  of  coast-line  has  been 
charted.  A  vast  archipelago  covers  this  part  of  the 
northern  world.  Or,  if  the  strangely-complicated  coast- 
lines which  have  been  laid  down  really  belong  to  but 
a  small  number  of  islands,  the  figures  of  these  must  be 
of  the  most  fantastic  kind.  Toward  the  northwest, 
however,  we  find  several  islands  whose  outlines  have 
been  entirely  ascertained.  Thus  we  have  in  succession 
North  Devon  Island,  Cornwallis  Island,  Melville  Island, 
and  Port  Patrick  Island,  all  lying  north  of  the  seventy- 
fifth  parallel  of  latitude.  But  we  are  not  to  suppose 
that  these  islands  limit  the  extent  of  our  seamen's 
researches  in  this  direction.  Far  to  the  northward  of 
Wellington  Channel,  Captain  de  Haven  saw,  in  1852, 
the  signs  of  an  open  sea — in  other  words,  he  saw,  be- 
yond the  ice-fields,  what  arctic  seamen  call  a  "  water- 
sky."  In  1855  Captain  Penny  sailed  upon  this  open 
sea ;  but  how  far  it  extends  toward  the  North  Pole  has 
not  yet  been  ascertained. 

It  must  not  be  forgotten  that  the  northwest  passage 
has  been  shown  to  be  a  reality,  by  means  of  voyages 
from  the  Pacific  as  well  as  from  the  Atlantic.  No  arctic 
voyager  has  yet  succeeded  in  passing  from  one  ocean 
to  the  other.  Nor  is  it  likely  now  that  any  voyager 
will  pursue  his  way  along  a  path  so  beset  by  dangers 
as  that  which  is  called  the  northwest  passage.  Long 


THE  SECRET   OF  THE  NORTH  POLE.  115 

before  the  problem  had  been  solved,  it  had  become  well 
known  that  no  profit  could  be  expected  to  accrue  to 
trade  from  the  discovery  of  a  passage  along  the  peril- 
ous straits  and  the  ice-encumbered  seas  which  lie  to 
the  north  of  the  American  Continent.  But  Sir  Edward 
Parry  having  traced  out  a  passage  as  far  as  Melville 
Island,  it  seemed  to  the  bold  spirit  of  our  arctic  ex- 
plorers that  it  might  be  possible,  by  sailing  through 
Behring's  Straits,  to  trace  out  a  connection  between 
the  arctic  seas  on  that  side  and  the  regions  reached  by 
Parry.  Accordingly,  McClure,  in  1850,  sailed  in  the 
"  Investigator,"  and  passing  eastward,  after  traversing 
Behring's  Straits,  reached  Baring's  Land,  and  event- 
ually identified  this  land  as  a  portion  of  Banks's  Land, 
seen  by  Parry  to  the  southward  of  Melville  Island. 

It  will  thus  be  seen  that  the  unexplored  parts  of  the 
arctic  regions  are  limited  in  this  direction  by  sufficient- 
ly high  latitudes. 

Turn  we  next  to  the  explorations  which  Russian 
voyagers  have  made  to  the  northward  of  Siberia.  It 
must  be  noticed,  in  the  first  place,  that  the  coast  of 
Siberia  runs  much  farther  northward  than  that  of  the 
American  Continent.  So  that  on  this  side,  indepen- 
dently of  sea  explorations,  the  unknown  arctic  regions 
are  limited  within  very  high  latitudes.  But  attempts 
have  been  made  to  push  much  farther  north  from  these 
shores.  In  every  case  however,  the  voyagers  have 
found  that  the  ice-fields,  over  which  they  hoped  to 


116  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

make  their  way,  have  become  gradually  less  and  less 
firm,  until  at  length  no  doubt  could  remain  that  there 

7  O 

lay  an  open  sea  beyond  them.  How  far  that  sea  may 
extend  is  a  part  of  the  secret  of  the  North  Pole ;  but 
we  may  assume  that  it  is  no  narrow  sea,  since  other- 
wise there  can  be  little  doubt  that  the  ice-fields  which 
surround  the  shores  of  Northern  Siberia  would  extend 
unbroken  to  the  farther  shores  of  what  we  should  thus 
have  to  recognize  as  a  strait.  The  thinning-ofF  of  these 
ice-fields,  observed  by  Baron  "Wrangel  and  his  com- 
panions, affords,  indeed,  most  remarkable  and  signifi- 
cant testimony  respecting  the  nature  of  the  sea  which 
lies  beyond.  This  we  shall  presently  have  to  exhibit 
more  at  length ;  in  the  mean  time  we  need  only  remark 
that  scarcely  any  doubt  can  exist  that  the  sea  thus 
discovered  extends  northward  to  at  least  the  eightieth 
parallel  of  latitude. 

"We  may  say,  then,  that  from  Wellington  Channel, 
northward  of  the  American  Continent,  right  round 
toward  the  west,  up  to  the  neighborhood  of  Spitz- 
bergen,  very  little  doubt  exists  as  to  the  general 
characteristics  of  arctic  regions,  save  only  as  respects 
those  unexplored  parts  which  lie  within  ten  or  twelve 
degrees  of  the  North  Pole.  The  reader  will  see  pres- 
ently why  we  are  so  careful  to  exhibit  the  limited 
extent  of  the  unexplored  arctic  regions  in  this  direction. 
The  guess  we  shall  form  as  to  the  true  nature  of  the 
north-polar  secret  will  depend  almost  entirely  on  this 
consideration. 


THE  SECRET  OF  THE  NORTH  POLE.  Hf 

We  turn  now  to  those  two  paths  along  which  arctic 
exploration,  properly  so  termed,  has  been  most  success- 
fully pursued. 

It  is  chiefly  to  the  expeditions  of  Drs.  .Kane  and 
Hayes  that  we  owe  the  important  knowledge  we  have 
respecting  the  northerly  portions  of  the  straits  which 
lie  to  the  west  of  Greenland.  Each  of  these  explorers 
succeeded  in  reaching  the  shores  of  an  open  sea  lying 
to  the  northeast  of  Kennedy  Channel,  the  extreme 
northerly  limit  of  those  straits.  Hayes,  who  had  ac- 
companied Kane  in  the  voyage  of  1854—'55,  succeeded 
in  reaching  a  somewhat  higher  latitude  in  sledges 
drawn  by  Esquimaux  dogs.  But  both  expeditions 
agree  in  showing  that  the  shores  of  Greenland  trend 
off  suddenly  toward  the  east  at  a  point  within  some 
nine  degrees  of  the  !N"orth  Pole.  On  the  other  hand, 
the  prolongation  of  the  opposite  shore  of  Kennedy 
Channel  was  found  to  extend  northward  as  far  as  the 
eye  could  reach.  Within  the  angle  thus  formed  there 
was  an  open  sea  "  rolling,"  says  Captain  Maury,  "  with 
the  swell  of  a  bound]ess  ocean." 

But  a  circumstance  was  noticed  respecting  this  sea 
which  was  very  significant.  The  tides  ebbed  and 
flowed  in  it.  Only  one  fact  we  know  of — a  fact  to 
be  presently  discussed — throws  so  much  light  on  the 
question  we  are  considering  as  this  circumstance  does. 
Let  us  consider  a  little  whence  these  tidal  waves  can 
have  come. 


118  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

The  narrow  straits  between  Greenland  on  the  one 
side,  and  Ellesmere  Land  and  Grinnell  Land  on  the 
other,  are  completely  ice-bound.  "We  cannot  suppose 
that  the  tidal  wave  could  have  found  its  way  beneath 
such  a  barrier  as  this.  "  I  apprehend,"  says  Captain 
Maury,  "that  the  tidal  wave  from  the  Atlantic  can 
no  more  pass  under  this  icy  barrier,  to  be  propagated 
in  the  seas  beyond,  than  the  vibrations  of  a  musical 
string  can  pass  with  its  notes  a  fret  on  which  the 
musician  has  placed  his  finger." 

Are  we  to  suppose,  then,  that  the  tidal  waves  were 
formed  in  the  very  sea  in  which  they  were  seen  by 
Kane  and  Hayes  ?  This  is  Captain  Maury's  opinion  : 
"  These  tides,"  says  he,  "  must  have  been  born  in  that 
cold  sea,  having  their  cradle  about  the  North  Pole." 

But  if  we  carefully  consider  the  theory  of  the  tides 
this  opinion  seems  inadmissible.  Every  consideration 
on  which  that  theory  is  founded  is  opposed  to  the 
assumption  that  the  moon  could  by  any  possibility 
raise  tides  in  an  arctic  basin  of  limited  extent.  It 
would  be  out  of  place  to  examine  at  length  the  prin- 
ciple on  which  the  formation  of  tides  depends.  It  will 
be  sufficient  for  our  purposes  to  remark  that  it  is  not 
to  the  mere  strength  of  the  moon's  "  pull "  upon  the 
waters  of  any  ocean  that  the  tidal  wave  owes  its  origin, 
but  to  the  difference  of  the  forces  by  which  the  various 
parts  of  that  ocean  are  attracted.  The  whole  of  an 
ocean  cannot  be  raised  at  once  by  the  moon ;  but  if 


THE  SECRET   OF  THE  NORTH  POLE.  HQ 

one  part  is  attracted  more  than  another,  a  wave  is 
formed.  That  this  may  happen,  the  ocean  must  be  one 
of  wide  extent.  In  the  vast  seas  which  surround  the 
Southern  Pole  there  is  room  for  an  immensely  powerful 
"  drag,"  so  to  speak ;  for  always  there  will  be  one  part 
of  these  seas  much  nearer  to  the  moon  than  the  rest, 
and  so  there  will  be  an  appreciable  difference  of  pull 
upon  that  part. 

The  reader  will  now  see  why  we  have  been  so  care- 
ful to  ascertain  the  limits  of  the  supposed  north-polar 
oceap,  in  which,  according  to  Captain  Maury,  tidal 
waves  are  generated.  To  accord  with  his  views,  this 
ocean  must  be  surrounded  on  all  sides  by  impassable 
barriers  either  of  land  or  ice.  These  barriers,  then, 
must  lie  to  the  northward  of  the  regions  yet  explored, 
for  there  is  open  sea  communicating  with  the  Pacific 
all  round  the  north  of  Asia  and  America.  It  only 
requires  a  moment's  inspection  of  a  terrestrial  globe  to 
see  how  small  a  space  is  thus  left  for  Captain  Maury's 
land-locked  ocean.  We  have  purposely  left  out  of 
consideration,  as  yet,  the  advances  made  by  arctic 
voyagers  in  the  direction  of  the  sea  which  lies  between 
Greenland  and  Spitzbergen.  "We  shall  presently  see 
that  on  this  side  the  imaginary  land-locked  ocean  must 
be  more  limited  than  toward  the  shores  of  Asia  or 
America.  As  it  is,  however,  it  remains  clear  that,  if 
there  were  any  ocean  communicating  with  the  spot 
reached  by  Dr.  Kane,  but  separated  from  all  commu- 


120  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

nication — by  open  water — either  with  the  Atlantic  or 
with  the  Pacific,  that  ocean  would  be  so  limited  in 
extent  that  the  moon's  attraction  could  exert  no  more 
effective  influence  upon  its  waters  than  upon  the 
waters  of  the  Mediterranean — where,  as  we  know,  no 
tides  are  generated.  This,  then,  would  be  a  tideless 
ocean,  and  we  must  look  elsewhere  for  an  explanation 
of  the  tidal  waves  seen  by  Dr.  Kane. 

We  thus  seem  to  have  prima  facie  evidence  that 
the  sea  reached  by  Kane  communicates  either  with  the 
Pacific  or  with  the  Atlantic,  or — which  is  the  most 
probable  view — with  both  those  oceans.  "When  we 
consider  the  voyages  which  have  been  made  toward 
the  North  Pole  along  the  northerly  prolongation  of 
the  Atlantic  Ocean,  we  find  very  strong  evidence  in 
favor  of  the  view  that  there  is  open-water  communica- 
tion in  this  direction,  not  only  with  the  spot  readied 
by  Kane,  but  with  a  region  very  much  nearer  to  the 
North  Pole. 

So  far  back  as  1GOT,  Hudson  had  penetrated  within 
8J°  (or  about  600  miles)  of  the  North  Pole  on  this 
route.  "When  we  consider  the  clumsy  build  and  the 
poor  sailing  qualities  of  the  ships  of  Hudson's  day,  we 
cannot  but  feel  that  so  successful  a  journey  marks  this 
route  as  one  of  the  most  promising  ever  tried.  Hudson 
was  not  turned  back  by  impassable  barriers  of  land  or 
ice,  but  by  the  serious  dangers  to  which  the  floating 
masses  of  ice  and  the  gradually-thickening  ice-fields 


THE   SECRET  OF  THE  NORTH  POLE.  121 

exposed  his  weak  and  ill-manned  vessel.     Since  his 
time,  others  have  sailed  upon  the  same  track,  and  hith- 
erto with  no  better  success.     It  has  been  reserved  to 
the  Swedish  expedition  of  last  year  to  gain  the  highest 
latitudes  ever  reached  in  a  ship  in  this  direction.     The 
steamship  "  Sofia,"  in  which  this  successful  voyage  was 
made,  was  strongly  built  of  Swedish  iron,  and  origi- 
nally intended  for  winter  voyages  in  the  Baltic.     Ow- 
ing to  a  number  of  delays,  it  was  not  until  September 
16th  that  the  "  Sofia  "  reached  the  most  northerly  part 
of  her  journey.     This  was  a  point  some  fifteen  miles 
nearer  the  North  Pole  than  Hudson  had  reached.     To 
the  north  there  still  lay  broken  ice,  but  packed  so  thick- 
ly that  not  even  a  boat  could  pass  through  it.     So  late 
in  the  season,  it  would  have  been  unsafe  to  wait  for  a 
change  of  weather  and  a  consequent  breaking  up  of 
the  ice.     Already  the  temperature  had  sunk  16°  below 
the  freezing-point ;  and  the  enterprising  voyagers  had 
no  choice  but  to  return.     They  made,  indeed,  another 
push  for  the  north  a  fortnight  later,  but  only  to  meet 
with  a  fresh  repulse.     An  ice-block  with  which  they 
came  into  collision  opened  a  large  leak  in  the  vessel's 
side  ;  and  when  after  great  exertions  they  reached  the 
land,  the  water  already  stood  two  feet  over  the  cabin- 
floor.     In  the  course  of  these  attempts,  the  depths  of 
the  Atlantic  were  sounded,  and  two  interesting  facts 
were  revealed.     The  first  was  that  the  island  of  Spitz- 
bergen  is  connected  with  Scandinavia  by  a  submarine 


122  LIGHT   SCIENCE  FOR  LEISURE  HOURS. 

bank ;  the  second  was  the  circumstance  that  to  the 
north  and  west  of  Spitzbergen  the  Atlantic  is  more 
than  two  miles  deep  ! 

We  come  now  to  the  most  conclusive  evidence  yet 
afforded  of  the  extension  of  the  Atlantic  Ocean  toward 
the  immediate  neighborhood  of  the  North  Pole.  Sin- 
gularly enough,  this  evidence  is  associated  not  with  a 
sea-voyage,  nor  with  a  voyage  across  ice  to  the  bor- 
ders of  some  northern  sea,  but  with  a  journey  during 
which  the  voyagers  were  throughout  surrounded  as  far 
as  the  eye  could  reach  by  apparently  fixed  ice-fields. 

In  1827  Sir  Edward  Parry  was  commissioned  by 
the  English  Government  to  attempt  to  reach  the 
North  Pole.  A  large  reward  was  promised  in  case 
he  succeeded,  or  even  if  he  could  get  within  five 
degrees  of  the  North  Pole.  The  plan  which  he 
adopted  seemed  promising.  Starting  from  a  port  in 
Spitzbergen,  he  proposed  to  travel  as  far  northward 
as  possible  in  sea-boats,  and  then,  landing  upon  the 
ice,  to  prosecute  his  voyage  by  means  of  sledges. 
Few  narratives  of  arctic  travel  are  more  interesting 
than  that  which  Parry  has  left  of  this  famous  "  boat- 
and-sledge"  expedition.  The  voyagers  were  terribly 
harassed  by  the  difficulties  of  the  way;  and,  after  a 
time,  that  most  trying  of  all  arctic  experiences,  the 
bitterly  cold  wind  which  comes  from  out  the  dreadful 
north,  was  added  to  their  trials.  Yet  still  they 
plodded  steadily  onward,  tracking  their  way  over 


THE  SECRET  OF  THE  NORTH  POLE.  123 

hundreds  of  miles  of  ice  with  the  confident  expecta- 
tion of  at  least  attaining  to  the  eighty-fifth  parallel,  if 
not  to  the  Pole  itself. 

But  a  most  grievous  disappointment  was  in  store 
for  them.  Parry  began  to  notice  that  the  astronomical 
observation  by  which  in  favorable  weather  he  estimated 
the  amount  of  their  northerly  progress,  showed  a  want 
of  correspondence  with  the  actual  rate  at  which  they 
were  travelling.  At  first  he  could  hardly  believe  that 
there  was  not  some  mistake ;  but  at  length  the  un- 
pleasing  conviction  was  forced  upon  him  that  the 
whole  ice-field  over  which  he  and  his  companions  had 
been  toiling  so  painfully  was  setting  steadily  southward 
before  the  wind.  Each  day  the  extent  of  this  set 
became  greater  and  greater,  until  at  length  they  were 
actually  carried  as  fast  toward  the  south  as  they  could 
travel  northward. 

Parry  deemed  it  useless  to  continue  the  struggle. 
There  were  certainly  two  chances  in  his  favor.  It 
was  possible  that  the  north  wind  might  cease  to  blow, 
and  it  was  also  possible  that  the  limit  of  the  ice  might 
soon  be  reached,  and  that  his  boats  might  travel  easily 
northward  upon  the  open  sea  beyond.  But  he  had  to 
consider  the  exhausted  state  of  his  men,  and  the  great 
additional  danger  to  which  they  were  subjected  by  the 
movable  nature  of  the  ice-fields.  If  the  ice  should 
break  up,  or  if  heavy  and  long-continued  southerly 
winds  should  blow,  they  might  have  found  it  very 


124  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

difficult  to  regain  tlieir  port  of  refuge  in  Spitzbergen 
before  winter  set  in  or  their  stores  were  exhausted. 
Besides,  there  were  no  signs  of  water  in  the  direction 
they  had  been  taking.  The  water-sky  of  arctic  regions 
can  be  recognized  by  the  experienced  seaman  long 
before  the  open  sea  itself  is  visible.  On  every  side, 
however,  there  were  the  signs  of  widely-extended  ice- 
fields. It  seemed,  therefore,  hopeless  to  persevere, 
and  Parry  decided  on  returning  with  all  possible  speed 
to  the  haven  of  refuge  prepared  for  the  party  in  Spitz- 
bergen. He  had  succeeded  in  reaching  the  highest 
northern  latitudes  ever  yet  attained  by  man. 

The  most  remarkable  feature  of  this  expedition, 
however,  is  not  the  high  latitude  which  the  party 
attained,  but  the  strange  circumstance  which  led  to 
their  discomfiture.  What  opinion  are  we  to  form  of 
an  ocean  at  once  wide  and  deep  enough  to  float  an 
ice-field  which  must  have  been  thirty  or  forty  thou- 
sand square  miles  in  extent?  Parry  had  travelled 
upward  of  three  hundred  miles  across  the  field,  and 
we  may  fairly  suppose  that  he  might  have  travelled 
forty  or  fifty  miles  farther  without  reaching  open 
water ;  also  that  the  field  extended  fully  fifty  miles  on 
each  side  of  Parry's  northerly  track.  That  the  whole 
of  so  enormous  a  field  should  have  floated  freely  before 
the  arctic  winds  is  indeed  an  astonishing  circumstance. 
On  every  side  of  this  floating  ice-island  there  must 
have  been  seas  comparatively  free  from  ice  ;  and  could 


THE   SECRET   OF  THE  NORTH  TOLE.  125 

a  stout  ship  have  forced  its  way  through  these  seas,  the 
latitudes  to  which  it  could  have  reached  would  have 
been  far  higher  than  those  to  which  Parry's  party  was 
able  to  attain.  For  a  moment's  consideration  will 
show  that  the  part  of  the  great  ice-field  where  Parry 
was  compelled  to  turn  back  must  have  been  floating 
in  far  higher  latitudes  when  he  first  set  out.  He 
reckoned  that  he  had  lost  more  than  a  hundred  miles 
through  the  southerly  motion  of  the  ice-field,  and  by 
this  amount,  of  course,  the  point  he  reached  had  been 
nearer  the  Pole.  It  is  not  assuming  too  much  to 
say  that  a  ship  which  could  have  forced  its  way  round 
the  great  floating  ice-field  would  certainly  have  been 
able  to  get  within  four  degrees  of  the  Pole.  It  seems 
to  us  highly  probable  that  she  would  even  have  been 
able  to  sail  upon  open  water  to  and  beyond  the  Pole 
itself. 

And  when  we  remember  the  direction  in  which  Dr. 
Kane  saw  an  open  sea — namely,  toward  the  very 
region  where  Parry's  ice-ship  had  floated  a  quarter  of 
a  century  before — it  seems  reasonable  to  conclude  that 
there  is  open-water  communication  between  the  seas 
which  lie  to  the  north  of  Spitzbergen  and  those  which 
lave  the  northwestern  shores  of  Greenland.  If  this 
be  so,  we  at  once  obtain  an  explanation  of  the  tidal 
waves  which  Kane  watched  day  after  day  in  1855. 
These  had  no  doubt  swept  along  the  valley  of  the 
Atlantic,  and  thence  around  the  northern  coast  of 


126  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

Greenland.  It  follows  that,  densely  as  the  ice  may 
be  packed  at  times  in  the  seas  by  which  Hudson, 
Scoresby,  and  other  captains,  have  attempted  to  reach 
the  North  Pole,  the  frozen  masses  must  in  reality  be 
floating  freely,  and  there  must  therefore  exist  channels 
through  which  an  adventurous  seaman  might  manage 
to  penetrate  the  dangerous  barriers  surrounding  the 
polar  ocean. 

In  such  an  expedition,  chance  unfortunately  plays 
a  large  part.  Whalers  tell  us  that  there  is  great  un- 
certainty as  to  the  winds  which  may  blow  during  an 
arctic  summer.  The  icebergs  may  be  crowded  by 
easterly  winds  upon  the  shores  of  Greenland,  or  by 
westerly  winds  upon  the  shores  of  Spitzbergen,  or, 
lastly,  the  central  passage  may  be  the  most  encum- 
bered, through  the  effects  of  winds  blowing  now  from 
the  east  and  now  from  the  west.  Thus  the  arctic 
voyager  has  not  merely  to  take  his  chance  as  to  the 
route  along  which  he  shall  adventure  northward,  but 
often,  after  forcing  his  way  successfully  for  a  consider- 
able distance,  he  finds  the  ice-fields  suddenly  closing 
in  upon  him  on  every  side,  and  threatening  to  crush 
his  ship  into  fragments.  The  irresistible  power  with 
which,  under  such  circumstances,  the  masses  of  ice 
bear  down  upon  the  stoutest  ship  has  been  evidenced 
again  and  again ;  though,  fortunately,  it  not  unfre- 
quently  happens  that  some  irregularity  along  one  side 
or  the  other  of  the  closing  channel  serves  as  a  sort  of 


THE   SECRET   OF  THE  NORTH  POLE.  127 

natural  dock,  within  which  the  vessel  may  remain  in 
comparative  safety  until  a  change  of  wind  sets  her 
free.  Instances  have  been  known  in  which  a  ship  has 
had  so  narrow  an  escape  in  this  way,  and  has  been 
subjected  to  such  an  enormous  pressure,  that  when  the 
channel  has  opened  out  again,  the  impress  of  the  ship's 
side  has  been  seen  distinctly  marked  upon  the  massive 
blocks  of  ice  which  have  pressed  against  her. 

Notwithstanding  the  dangers  and  difficulties  of  the 
attempt,  and  the  circumstance  that  no  material  gains 
can  reward  the  explorer,  it  seems  not  unlikely  that 
before  many  months  are  passed  the  North  Pole  will 
have  been  reached.  Last  year  two  bold  attempts  were 
made — one  by  the  Swedes,  as  already  mentioned,  the 
other  by  German  men  of  science.  In  each  case  the 
result  was  so  far  successful  as  to  give  good  promise  for 
future  attempts.  This  year  both  these  nations  will 
renew  their  attack  upon  the  interesting  problem.  The 
German  expedition  will  consist  of  two  vessels,  the 
"  Germania  "  and  the  "  Greenland."  The  former  is  a 
screw-steamer,  of  126  tons,  and  well  adapted  to  en- 
counter the  buffets  of  the  ice-masses  which  are  borne 
upon  the  arctic  seas.  The  other  is  a  sailing-yacht  of 
80  tons,  and  is  intended  to  act  as  a  transport-ship,  by 
means  of  which  communication  may  be  kept  up  with 
Europe.  The  "  Germania "  will  probably  winter  in 
high  northern  latitudes ;  and  we  should  not  be  much 
surprised  if  before  her  return  she  should  have  been 


128  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

carried  to  the  very  Pole.  'Nor  can  tlie  prospects  of  the 
Swedish  expedition  be  considered  less  promising,  when 
we  remember  that  last  year,  though  hampered  by  the 
lateness  of  the  season  and  other  difficulties,  they  suc- 
ceeded in  approaching  the  Pole  within  a  distance  only 
a  few  miles  greater  than  that  which  separated  Parry 
from  the  Pole  in  1829. 

Certainly  England  has  reason  to  feat  that  before 
the  year  1870  has  closed  she  will  no  longer  be  able  to 
claim  that  her  flag  has  approached  both  Poles  more 
nearly  than  the  flag  of  any  other  nation.  There  are 
considerations  which  make  the  recent  eupineness  of 
our  country  in  the  matter  of  arctic  travel  much  to  be 
regretted.  In  the  winter  of  1874  there  will  occur  one 
of  those  interesting  phenomena  by  which  Nature  oc- 
casionally teaches  men  useful  lessons  respecting  her 
economy.  We  refer  to  the  transit  of  Venus  on  De- 
cember 8th  in  that  year.  One  of  the  most  effective 
modes  of  observing  this  transit  will  require  that  a 
party  of  scientific  men  should  penetrate  far  within  the 
recesses  of  the  desolate  Antarctic  Circle.  "Where  are 
the  trained  arctic  seamen  to  be  found  who  will  venture 
upon  this  service  ?  Most  of  our  noted  arctic  voyagers 
have  earned  their  rest ;  and,  as  Commander  Davis  said 
at  a  recent  meeting  of  the  Geographical  Society,  those 
who  go  for  the  first  time  into  the  arctic  or  antarctic 
solitudes  are  too  much  tried  by  the  effects  of  the  new 
experience  to  be  fit  to  undertake  important  scientific 


IS  THE   GULF  STREAM  A  MYTH?  129 

labors.  He  spoke  with  special  reference  to  tlie  transit 
of  1882,  for  the  observation  of  which  there  is  (I  have 
lately  shown)  small  occasion  to  employ  arctic  voyagers. 
It  is  just  possible  that  for  the  transit  of  18Y4  trained 
explorers  belonging  to  the  old  school  of  arctic  travel 
may  still  be  found.  But  if  not,  no  time  should  be  lost 
in  supplying  the  deficiency.  I  have  shown  within  the 
last  few  months  that  journeys  to  the  antarctic  regions 
will  be  required  for  this  transit,  and  not  for  the  later 
transit  (as  had  been  supposed).  The  Astronomer- 
Hoy  al  has  expressed  his  desire  that  the  discovery  may 
be  rendered  available  by  suitable  expeditions.  "  Every 
series  of  observations,"  he  remarks,  "  which  can  really 
be  brought  to  bear  upon  this  important  determination 
will  be  valuable."  Therefore,  for  this  reason  alone, 
and  even  if  the  reputation  of  England  in  the  matter  of 
arctic  travel  were  altogether  worthless,  it  would  be 
well  that  efforts  should  quickly  be  made  to  prepare 
crews  and  commanders  for  the  work  of  1874,  by 
"  sending  them  to  school,"  as  Commander  Davis  ex- 
pressed it,  "  in  the  arctic  seas." 

(From  St.  Paul's,  June,  1869.) 


IS   THE  GULF  STREAM  A   MYTH? 

THE  Gulf  Stream  has  recently  attracted  a  large 
share  of  the  attention  of  our  men  of  science.  The 
abnormal  character  of  the  weather  which  we  experi- 


130  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

enced  last  winter  has  had  something  to  do  with  this. 
The  influence  of  the  Gulf  Stream  upon  our  climate, 
and  the  special  influence  which  it  is  assumed  to  exer- 
cise in  mitigating  the  severity  of  our  winters,  have 
been  so  long  recognized  that  meteorologists  began  to 
inquire  what  changes  could  be  supposed  to  have  taken 
place  in  the  great  current  to  account  for  so  remarkable 
a  winter  as  the  last.  But  it  happened  also  that  at  a 
meeting  of  the  Royal  Geographical  Society  early  in 
the  present  year  the  very  existence  of  the  Gulf  Stream 
was  called  in  question,  just  when  meteorologists  were 
disposed  to  assign  to  it  effects  of  unusual  importance. 
And  in  the  course  of  the  discussion  whether  there  is  in 
truth  a  Gulf  Stream — or  rather  whether  our  shores  are 
visited  by  a  current  which  merits  such  a  name — a 
variety  of  interesting  facts  were  adduced,  which  were 
either  before  unknown  or  had  attracted  little  attention. 
As  at  a  recent  meeting  of  the  same  society  these  doubts 
have  been  renewed,  we  propose  to  examine  briefly,  in 
the  first  place,  a  few  of  the  considerations  which  have 
been  urged  against  the  existence  of  a  current  from  the 
Gulf  of  Mexico  to  the  neighborhood  of  our  shores ; 
and  then,  having  rehabilitated  the  reputation  of  this 
celebrated  ocean-river — as  we  believe  we  shall  be  able 
to  do — we  shall  proceed  to  give  a  brief  sketch  of  the 
processes  by  which  the  current-system  of  the  North 
Atlantic  is  set  and  maintained  in  motion. 

In  reality  the  Gulf  Stream  is   only  a  part  of  a 


IS  THE   GULF  STREAM  A  MYTH?  131 

system  of  oceanic  circulation ;  but  in  dealing  with 
the  arguments  which  have  been  urged  against  its  very 
existence,  we  may  conline  our  attention  to  the  fact 
that,  according  to  the  views  which  had  been  accepted 
for  more  than  a  century,  there  is  a  stream  of  water 
which,  running  out  of  the  Gulf  Stream  through  the 
Narrows  of  Bernini,  flows  along  the  shores  of  the 
United  States  to  Newfoundland,  and  thence  right 
across  the  Atlantic  to  the  shores  of  Great  Britain. 
It  is  this  last  fact  which  is  now  called  in  question. 
The  existence  of  a  current  as  far  as  the  neighbor- 
hood of  Newfoundland  is  conceded,  but  the  fact  that 
the  stream  flows  onward  to  our  shores  is  denied. 

The  point  on  which  the  most  stress  is  placed  is  the 
shallowness  of  the  passage  called  the  "  Bernini  Nar- 
rows," through  which  it  is  assumed  that  the  whole  of 
the  Gulf  current  must  pass.  This  passage  has  a  width 
of  about  forty  miles,  and  a  depth  of  a  little  more  than 
six  hundred  yards.  The  current  which  flows  through 
it  is  perhaps  little  more  than  thirty  miles  in  width, 
and  a  quarter  of  a  mile  in  depth.  It  is  asked  with 
some  appearance  of  reason,  how  this  narrow  current 
can  be  looked  upon  as  the  parent  of  that  wide  stream, 
which  is  supposed  to  traverse  the  Atlantic  with  a  mean 
width  of  some  five  or  six  hundred  miles.  Indeed,  a 
much  greater  width  has  been  assigned  to  it,  though  on 
mistaken  grounds  ;  for  it  has  been  remarked  that  since 
waifs  and  strays  from  the  tropics  are  found  upon  the 


132  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

shores  of  Portugal,  as  well  as  upon  those  of  Greenland, 
we  must  ascribe  to  the  current  a  span  equal  to  the 
enormous  space  separating  these  places.  But  the 
circumstance  here  dwelt  upon  can  clearly  be  explained 
in  another  way.  "We  know  that  of  two  pieces  of  wood 
thrown  into  the  Thames  at  Richmond,  one  might  be 
picked  up  at  Putney,  and  the  other  at  Gravesend. 
Yet  we  do  not  conclude  that  the  width  of  the  Thames 
is  equal  to  the  distance  separating  Putney  from  Graves- 
end.  And  doubtless  the  tropical  waifs  which  have  been 
picked  up  on  the  shores  of  Greenland  and  of  Portugal 
have  found  their  way  thither  by  circuitous  courses,  and 
not  by  direct  transmission  along  opposite  edges  of  the 
great  Gulf  current. 

But  certainly  the  difficulty  associated  with  the  nar- 
rowness of  the  Bernini  current  is  one  deserving  of 
careful  attention.  Are  we  free  to  identify  a  current 
six  hundred  miles  in  width  with  one  ^vrhich  is  but 
thirty  miles  wide,  and  not  very  deep  ?  An  increase  of 
width  certainly  not  less  than  thirtyfold  would  appear 
to  correspond  to  a  proportionate  diminution  of  depth. 
And  remembering  that  it  is  only  near  the  middle  of 
the  Narrows  that  the  Gulf  Stream  has  a  depth  of  four 
hundred  yards,  we  could  scarcely  assign  to  the  wide 
current  in  the  mid-Atlantic  a  greater  depth  than  ten 
or  twelve  yards.  This  depth  seems  altogether  out  of 
proportion  to  the  enormous  lateral  extension  of  the 
current. 


IS  THE   GULF  STREAM  A  MYTH?  133 

But  besides  that  even  this  consideration  would  not 
suffice  to  disprove  the  existence  of  a  current  in  the 
mid- Atlantic,  an  important  circumstance  remains  to  be 
mentioned.  The  current  in  the  JSTarrows  flows  with 
great  velocity — certainly  not  less  than  four  or  five 
miles  an  hour.  As  the  current  grows  wider  it  flows 
more  sedately ;  and  opposite  Cape  Hatteras  its  velocity 
is  already  reduced  to  little  more  than  three  miles  an 
hour.  In  the  mid-Atlantic  the  current  may  be  assumed 
to  flow  at  a  rate  little  exceeding  a  mile  per  hour,  at 
the  outside.  Here,  then,  we  have  a  circumstance 
which  suffices  to  remove  a  large  part  of  the  difficulty 
arising  from  the  narrowness  of  the  Bernini  current, 
and  we  can  at  once  increase  our  estimate  of  the  depth 
of  the  mid- Atlantic  current  fivefold. 

But  this  is  not  all.  It  has  long  been  understood 
that  the  current  which  passes  out  through  the  Narrows 
of  Bernini  corresponds  to  the  portion  of  the  great 
equatorial  current  which  passes  into  the  Gulf  of 
Mexico  between  the  West-Indian  Islands.  "We  cannot 
doubt  that  the  barrier  formed  by  those  islands  serves  to 
divert  a  large  portion  of  the  equatorial  current.  The 
portion  thus  diverted  finds  its  way,  we  may  assume, 
along  the  outside  of  the  West-Indian  Archipelago, 
and  thus  joins  the  other  portion — w^hich  has  in  the 
mean  time  made  the  circuit  of  the  Gulf — as  it  issues 
from  the  Bernini  Straits.  All  the  maps  in  which  the 
Atlantic  currents  are  depicted  present  precisely  such" 


134  LIGHT   SCIENCE  FOR  LEISURE  HOURS. 

an  outside  current  as  we  liave  here  spoken  of,  and 
most  of  them  assign  to  it  a  width  exceeding  that  of 
the  Bernini  current.  Indeed,  were  it  not  for  the 
doubts  which  the  recent  discussions  have  thrown  upon 
all  the  currents  charted  by  seamen,  we  should  have 
been  content  to  point  to  this  outside  current  as  shown 
in  the  maps.  As  it  is,  we  have  thought  it  necessary  to 
show  that  such  a  current  must  necessarily  have  an 
existence,  since  we  cannot  lose  sight  of  the  influence 
of  the  West-Indian  Isles  in  partially  damming  up  the 
passage  along  which  the  equatorial  current  would 
otherwise  find  its  way  into  the  Gulf  of  Mexico. 
Whatever  portion  of  the  great  current  is  thus 
diverted  must  find  a  passage  elsewhere,  and  no  pas- 
sage exists  for  it  save  along  the  outside  of  the  West- 
Indian  Isles. 

The  possibility  that  the  wide  current  which  has 
been  assumed  to  traverse  the  mid- Atlantic  may  be 
associated  with  the  waters  which  flow  from  the  Gulf 
of  Mexico,  either  through  the  Narrows  or  round  the 
outside  of  the  barrier  formed  by  the  West  Indies,  has 
thus  been  satisfactorily  established.  But  we  now  have 
to  consider  difficulties  which  have  been  supposed  to 
encounter  our  current  on  its  passage  from  the  Gulf  to 
the  mid- Atlantic. 

Northward,  along  the  shores  of  the  United  States, 
the  current  has  been  traced  by  the  singular  blueness 
of  its  waters  until  it  has  reached  the  neighborhood  of 


IS  THE   GULF  STREAM  A  MYTH?  135 

Newfoundland.  Over  a  part  of  this  course,  indeed, 
the  waters  of  the  current  are  of  indigo  blue,  and  so 
clearly  marked  that  their  line  of  junction  with  the 
ordinary  sea-water  can  be  traced  by  the  eye.  "  Often," 
says  Captain  Maury,  "one  half  of  a  vessel  may  be 
perceived  floating  in  Gulf-Stream  water,  while  the 
other  half  is  in  common  water  of  the  sea — so  sharp  is 
the  line,  and  such  the  want  of  affinity  between  the 
waters,  and  such,  too,  the  reluctance,  so  to  speak,  on 
the  part  of  those  of  the  Gulf  Stream  to  mingle  with 
the  littoral  waters  of  the  sea." 

But  it  is  now  denied  that  there  is  any  current  be- 
yond the  neighborhood  of  Newfoundland — or  that 
the  warm  temperature,  which  has  characterized  the 
waters  of  the  current  up  to  this  point,  can  be  detected 
farther  out. 

It  is  first  noticed  that,  as  the  Gulf  current  must 
reach  the  neighborhood  of  Newfoundland  with  a  north- 
easterly motion,  and,  if  it  ever  reached  the  shores  of 
the  British  Isles,  would  have  to  travel  thither  with 
an  almost  due  easterly  motion,  there  is  a  change  of 
direction  to  be  accounted  for.  This,  however,  is  an 
old,  and  we  had  supposed  exploded,  fallacy.  The 
course  of  the  Gulf  Stream  from  the  Bernini  Straits  to 
the  British  Isles  corresponds  exactly  with  that  which 
is  due  to  the  combined  effects  of  the  motion  of  the 
water  and  that  of  the  earth  upon  its  axis.  Florida 
being  much  nearer  than  Ireland  to  the  equator,  has  a 


136  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

much  more  rapid  easterly  motion.  Therefore,  as  tlie 
current  gets  farther  and  farther  north,  the  effect  of  the 
easterly  motion  thus  imparted  to  it  begins  to  show 
itself  more  and  more,  until  the  current  is  gradually 
changed  from  a  northeasterly  to  an  almost  .easterly 
stream.  The  process  is  the  exact  converse  of  that  by 
which  the  air-currents  from  the  north  gradually  change 
into  the  northwesterly  trade- winds  as  they  get  farther 
south. 

But  it  is  further  remarked  that  as  the  current 
passes  out  beyond  the  shelter  of  Newfoundland,  it  is 
impinged  upon  by  those  cold  currents  from  the  arctic 
seas  which  are  known  to  be  continually  flowing  out 
of  Baffin's  Bay  and  down  the  eastern  shores  of  Green- 
land ;  and  it  is  contended  that  these  currents  suffice, 
not  merely  to  break  up  the  Gulf  current,  but  so  to 
cool  its  waters  that  these  could  produce  no  effect  upon 
the  climate  of  Great  Britain  if  they  ever  reached  its 
neighborhood. 

Here,  again,  we  must  remark  that  we  are  dealing 
with  no  new  discovery.  Captain  Maury  has  already 
remarked  upon  this  peculiarity.  "  At  the  very  season 
of  the  year,"  he  says,  "  when  the  Gulf  Stream  is  rush- 
ing in  greatest  volume  through  the  Straits  of  Florida, 
and  hastening  to  the  north  with  the  greatest  rapidity, 
there  is  a  cold  stream  from  Baffin's  Bay,  Labrador, 
and  the  coasts  of  the  north,  running  south  with  equal 
velocity.  ....  One  part  of  it  underruns  the  Gulf 


IS  THE   GULF  STREAM  A  MYTH?  137 

Stream,  as  is  sliown  by  the  icebergs,  wliicli  are  carried 
in  a  direction  tending  across  its  course."  There  can 
be  no  doubt,  in  fact,  that  this  last  circumstance  indi- 
cates the  manner  in  which  the  main  contest  between 
the  two  currents  is  settled.  A  portion  of  the  arctic 
current  finds  its  way  between  the  Gulf  Stream  and 
the  continent  of  America ;  and  this  portion,  though 
narrow,  has  a  very  remarkable  effect  in  increasing  the 
coldness  of  the  American  winters.  But  the  main  part, 
heavier,  by  reason  of  its  coldness,  than  the  surround- 
ing water,  sinks  beneath  the  surface.  And  the  well- 
known  fact  mentioned  by  Maury,  that  icebergs  have 
been  seen  stemming  the  Gulf  Stream,  suffices  to  show 
how  comparatively  shallow  that  current  is  at  this  dis- 
tance from  its  source,  and  thus  aids  to  remove  a  diffi- 
culty which  we  have  already  had  occasion  to  deal  with. 
Doubtless  the  cooling  influence  of  the  arctic  cur- 
rents is  appreciable;  but  it  would  be  a  mistake  to 
suppose  that  this  influence  can  suffice  to  deprive  the 
Gulf  current  of  its  distinctive  warmth.  If  all  the 
effect  of  the  cold  current  were  operative  on  the  Gulf 
Stream  alone,  we  might  suppose  that,  despite  the 
enormous  quantity  of  comparatively  warm  water  which 
is  continually  being  carried  northward,  the  current 
would  be  reduced  to  the  temperature  of  the  surround- 
ing water.  But  this  is  not  so.  The  arctic  current 
not  only  cools  the  Gulf  current,  but  the  surrounding 
water  also — possibly  to  a  greater  extent,  for  it  is  com- 


138  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

monly  supposed  that  a  bed  of  ordinary  sea -water 
separates  the  two  main  currents  from  each  other. 
Thus  the  characteristic  difference  of  temperature  re- 
mains unaffected.  But  in  reality  we  may  assume  that 
the  cooling  effect  actually  exercised  by  the  arctic  cur- 
rent upon  the  neighboring  sea  is  altogether  dispropor- 
tionate to  the  immense  amount  of  heat  continually 
being  carried  northward  by  the  Gulf  Stream.  It  is 
astonishing  how  unreadily  two  sea-currents  exchange 
their  temperatures — to  use  a  somewhat  inexact  mode 
of  expression.  The  very  fact  that  the  littoral  current 
of  the  United  States  is  so  cold — a  fact  thoroughly 
established — shows  how  little  warmth  this  current  has 
drawn  from  the  neighboring  seas.  Another  fact,  men- 
tioned by  Captain  Maury,  bears  in  a  very  interesting 
manner  upon  this  peculiarity.  He  says :  "  If  any 
vessel  will  take  up  her  position  a  little  to  the  north- 
ward of  Bermuda,  and  steering  thence  for  the  capes 
of  Virginia,  will  try  the  water-thermometer  all  the 
way  at  short  intervals,  she  will  find  its  reading  to  be 
now  higher,  now  lower ;  and  the  observer  will  dis- 
cover that  he  has  been  crossing  streak  after  streak  of 
warm  and  cool  water  in  regular  alternations."  Each 
portion  maintains  its  own  temperature  even  in  the 
case  of  such  warm  streaks  as  these,  all  belonging  to 
one  current. 

Similar   considerations   dispose   of  the   arguments 
which  have  been  founded  on  the  temperature  of  the 


IS  THE   GULF  STREAM  A  MYTH?  139 

sea-bottom.  It  has  been  proved  that  the  living  crea- 
tures which  people  the  lower  depths  of  the  sea  exist 
under  circumstances  which  evidence  a  perfect  uni- 
formity of  temperature  ;  and  arguments  on  the  subject 
of  the  Gulf  Stream  have  been  derived  from  the  evi- 
dence of  what  is  termed  a  minimum  thermometer — • 
that  is,  a  thermometer  which  will  indicate  the  lowest 
temperature  it  has  been  exposed  to — let  down  into  the 
depths  of  the  sea.  All  such  arguments,  whether  ad- 
duced against  or  in  favor  of  the  Gulf-Stream  theory, 
must  be  held  to  be  futile,  since  the  thermometer  in  its 
descent  may  pass  through  several  submarine  currents 
of  different  temperature. 

Lastly,  an  argument  has  been  urged  against  the 
warming  effects  of  the  Gulf  Stream  upon  our  climate, 
which  requires  to  be  considered  with  some  attention. 
It  is  urged  that  the  warmth  derived  from  so  shallow  a 
current  as  the  Gulf  Stream  must  be,  by  the  time  it  has 
reached  our  shores,  could  not  provide  an  amount  of 
heat  sufficient  to  affect  our  climate  to  any  appreciable 
extent.  The  mere  neighborhood  of  this  water  at  a 
temperature  slightly  higher  than  that  due  to  the  lati- 
tude could  not,  it  is  urged,  affect  the  temperature  of 
the  inland  counties  at  all. 

This  argument  is  founded  on  a  misapprehension  of 
the  beautiful  arrangement  by  which  Nature  carries  heat 
from  one  region  to  distribute  it  over  another.  Over 
the  surface  of  the  whole  current  the  process  of  evapo- 


140  LIGHT   SCIENCE  FOR  LEISURE   HOURS. 

ration  is  going  on  at  a  greater  rate  than  over  the  neigh- 
boring seas,  because  the  waters  of  the  current  are 
warmer  than  those  which  surround  them.  The  vapor 
thus  rising  above  the  Gulf  Stream  is  presently  wafted 
by  the  southwesterly  winds  to  our  shores  and  over  our 
whole  land.  But  as  it  thus  reaches  a  region  of  com- 
parative cold  the  vapor  is  condensed — that  is,  turned 
into  fog,  or  mist,  or  cloud,  according  to  circumstances. 
It  is  during  this  change  that  it  gives  out  the  heat  it 
has  brought  with  it  from  the  Gulf  Stream.  For  pre- 
cisely as  the  evaporation  of  water  is  a  process  requiring 
heat,  the  change  of  vapor  into  water — whether  in  the 
form  of  fog,  mist,  cloud,  or  rain — is  a  process  in  which 
heat  is  given  out.  Thus  it  is  that  the  southwesterly 
wind,  the  commonest  wind  we  have,  brings  clouds  and 
fogs  and  rain  to  us  from  the  Gulf  Stream,  and  with 
them  brings  the  Gulf-Stream  warmth. 

"Why  the  southwesterly  winds  should  be  so  common, 
and  how  it  is  that  over  the  Gulf  Stream  there  is  a  sort 
of  air-channel  along  which  winds  come  to  us  as  if  by 
their  natural  pathway,  we  have  not  space  here  to 
inquire  (see  p.  183).  The  subject  is  full  of  interest,  but 
it  does  not  belong  to  the  question  we  are  considering. 

It  would  seem  that  a  mechanism  involving  the 
motion  of  such  enormous  masses  of  water  as  the 
current-system  of  the  Atlantic  should  depend  on  the 
operation  of  very  evident  laws.  Yet  a  variety  of  con- 
tradictory hypotheses-  have  been  put  forward  from  time 


IS  THE   GULF  STREAM  A  MYTH?  141 

to  time  respecting  tins  system  of  circulation,  and  even 
now  the  scientific  world  is  divided  between  two  oppos- 
ing theories. 

Of  old  the  Mississippi  River  was  supposed  to  be  the 
parent  of  the  Gulf  Stream.  It  was  noticed  that  the 
current  flows  at  about  the  same  rate  as  the  Mississippi, 
and  this  fact  was  considered  sufficient  to  support  the 
strange  theory  that  a  river  can  give  birth  to  an  ocean- 
current. 

It  was  easy,  however,  to  overthrow  this  theory. 
Captain  Livingston  showed  that  the  volume  of  water 
which  is  poured  out  of  the  Gulf  of  Mexico  in  the  form 
of  an  ocean-stream  is  more  than  a  thousand  times 
greater  than  the  volume  poured  into  the  Gulf  by  the 
Mississippi  River. 

Having  overthrown  this  old  theory  of  the  Gulf 
Stream,  Captain  Livingston  attempted  to  set  up  one 
which  is  equally  unfounded.  He  ascribed  the  current 
to  the  sun's  apparent  yearly  motion  and  the  influence 
he  exerts  on  the  waters  of  the  Atlantic.  A  sort  of 
yearly  tide  is  conceived,  according  to  this  theory,  to  be 
the  true  parent  of  the  Gulf  current.  It  need  hardly 
be  said,  however,  that  a  phenomenon  which  remains 
without  change  through  the  winter  and  summer  seasons 
cannot  possibly  be  referred  to  the  operation  of  such  a 
cause  as  a  yearly  tide. 

It  is  to  Dr.  Franklin  that  we  owe  the  first  theory  of 
the  Gulf  Stream  which  has  met  with  general  acceptance. 


142  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

He  held  that  the  Gulf  Stream  is  formed  by  the  outflow 
of  waters  which  have  been  forced  into  the  Caribbean 
Sea  by  the  trade-winds ;  so  that  the  pressure  of  these 
winds  on  the  Atlantic  Ocean  forms,  according  to  Dr. 
Franklin,  the  true  motive  power  of  the  Gulf-Stream 
machinery.  According  to  Maury,  this  theory  has 
"  come  to  be  the  most  generally-received  opinion  in  the 
mind  of  seafaring  people."  It  supplies  a  moving  force 
of  undoubted  efficiency.  "We  know  that,  as  the  trade- 
winds  travel  toward  the  equator,  they  lose  their  west- 
erly motion.  It  is  reasonable  to  suppose  that  this  is 
caused  by  friction  against  the  surface  of  the  ocean,  to 
which,  therefore,  a  corresponding  westerly  motion  must 
have  been  imparted. 

There  is  a  simplicity  about  Franklin's  theory  which 
commends  it  favorably  to  our  consideration.  But 
when  we  examine  it  somewhat  more  closely,  several 
very  decided  flaws  present  themselves  to  our  attention. 

Consider,  in  the  first  place,  the  enormous  mass  of 
water  moved  by  the  supposed  agency  of  the  winds. 
Air  has  a  weight — volume  for  volume — which  is  less 
than  one  eight-hundredth  part  of  that  of  water.  So 
that,  to  create  a  water-current,  an  air-current  more 
than  eight  hundred  times  as  large  and  of  equal  velocity 
must  expend  the  whole  of  its  motion.  JSTow,  the  trade- 
winds  are  gentle  winds,  their  velocity  scarcely  exceed- 
ing in  general  that  of  the  more  swiftly-moving  portions 
of  the  Gulf  Stream.  But  even  assigning  to  them  a 


IS  THE  GULF  STREAM  A  MYTH?  143 

velocity  four  times  as  great,  we  still  want  an  air-current 
two  hundred  times  as  large  as  the  water-current.  And 
the  former  must  give  up  the  whole  of  its  motion,  which, 
in  the  case  of  so  elastic  a  substance  as  air,  would  hardly 
happen,  the  upper  air  being  unlikely  to  be  much 
affected  by  the  motion  of  the  lower. 

But  this  is  far  from  being  all.  If  the  trade-winds 
blew  throughout  the  year,  we  might  be  disposed  to 
recognize  their  influence  upon  the  Gulf  Stream  as  a 
paramount,  if  not  the  sole  one.  But  this  is  not  the 
case.  Captain  Maury  states  that,  "  with  the  view  of 
ascertaining  the  average  number  of  days  during  the 
year  that  the  northeast  trade-winds  of  the  Atlantic 
operate  upon  the  currents  between  25-°  north  latitude 
and  the  equator,  log-books  containing  no  less  than 
380,284  observations  on  the  force  and  direction  of 
the  wind  in  that  ocean  were  examined.  The  data 
thus  afforded  were  carefully  compared  and  discussed. 
The  results  show  that  within  these  latitudes — and 
on  the  average — the  wind  from  the  northeast  is  in 
excess  of  the  winds  from  the  southwest  only  111 
days  out  of  the  365.  Now,  can  the  northeast  trades," 
he  pertinently  asks,  "  by  blowing  for  less  than  one- 
third  of  the  time,  cause  the  Gulf  Stream  to  run  all  the 
time,  and  without  varying  its  velocity  either  to  their 
force  or  to  their  prevalence?" 

And  besides  this,  we  have  to  consider  that  no  part 
of  the  Gulf  Stream  flows  strictly  before  the  trade- 


144  LIGHT   SCIENCE  FOR  LEISURE  HOURS. 

winds.  Where  the  current  flows  most  rapidly,  namely, 
in  the  Narrows  of  Bernini,  it  sets  against  the  wind,  and 
for  hundreds  of  miles  after  it  enters  the  Atlantic,  "  it 
runs,"  says  JVIaury,  "  right  in  the  '  wind's  eye.'  "  It 
must  be  remembered  that  a  current  of  air  directed 
with  considerable  force  against  the  surface  of  still 
wrater  has  not  the  power  of  generating  a  current  which 
can  force  its  way  far  through  the  resisting  fluid.  If 
this  were  so,  we  might  understand  how  the  current, 
originating  in  sub-tropical  regions,  could  force  its  way 
onward  after  the  moving  force  had  ceased  to  act  upon 
it,  and  even  carry  the  waters  of  the  current  right 
against  the  wind,  after  leaving  the  Gulf  of  Mexico. 
But  experience,  is  wrholly  opposed  to  this  view.  The 
most  energetic  currents  are  quickly  dispersed  when 
they  reach  a  wide  expanse  of  still  water.  For  example, 
the  Niagara  below  the  falls  is  an  immense  and  rapid 
river.  Yet  when  it  reaches  Lake  Ontario,  "  instead  of 
preserving  its  character  as  a  distinct  and  well-defined 
stream  for  several  hundred  miles,  it  spreads  itself  out, 
and  its  wraters  are  immediately  lost  in  those  of  the 
lake."  Here,  again,  the  question  asked  by  Maury 
bears  pertinently  on  the  subject  we  are  considering. 
"  Why,"  he  says,  "  should  not  the  Gulf  Stream  do  the 
same  ?  It  gradually  enlarges  itself,  it  is  true ;  but, 
instead  of  mingling  with  the  ocean  by  broad  spread- 
ing, as  the  immense  rivers  descending  into  the  northern 
lakes  do,  its  waters,  like  a  stream  of  oil  in  the  ocean, 


IS  THE  GULF  STREAM  A  MYTH?  145 

preserve  a  distinctive  character  for  more  than  three 
thousand  miles." 

The  only  other  theory  which  has  been  considered  in 
recent  times  to  account  satisfactorily  for  all  the  features 
of  the  Gulf-Stream  mechanism  was  put  forward,  we 
believe,  by  Captain  Maury.  In  this  theory,  the  motive 
power  of  the  whole  system  of  oceanic  circulation  is 
held  to  be  the  action  of  the  sun's  heat  upon  the  waters 
of  the  sea.  We  recognize  two  contrary  effects  as  the 
immediate  results  of  the  sun's  action.  In  the  first 
place,  by  warming  the  equatorial  waters,  it  tends  to 
make  them  lighter ;  in  the  second  place,  by  causing 
evaporation,  it  renders  them  salter,  and  so  tends  to 
make  them  heavier.  We  have  to  inquire  which  form 
of  action  is  most  effective.  The  inquiry  would  be  some- 
what difficult,  if  we  had  not  the  evidence  of  the  sea 
itself  to  supply  an  answer.  For  it  is  an  inquiry  to 
which  ordinary  experimental  processes  would  not  be 
applicable.  "We  must  accept  the  fact  that  the  heated 
water  from  the  equatorial  seas  actually  does  float  upon 
the  cooler  portions  of  the  Atlantic,  as  evidence  that  the 
action  of  the  sun  results  in  making  the  water  lighter. 

Now,  Maury  says  that  the  water  thus  lightened 
must  flow  over  and  form  a  surface-current  toward  the 
Poles ;  while  the  cold  and  heavy  water  from  the  polar 
seas,  as  soon  as  it  reaches  the  temperate  zone,  must 
sink  and  form  a  submarine  current.  He  recognizes  in 
these  facts  the  mainspring  of  the  whole  system  of 


146  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

oceanic  circulation.  If  a  long  trough  be  divided  into 
two  compartments,  and  we  iill  one  with  oil  and  the 
other  with  water,  and  then  remove  the  dividing  plate, 
we  shall  see  the  oil  rushing  over  the  water  at  one  end 
of  the  trough,  and  the  water  rushing  under  the  oil  at 
the  other.  And  if  we  farther  conceive  that  oil  is  con- 
tinually being  added  at  that  end  of  the  trough  origi- 
nally filled  with  oil,  while  water  is  continually  added 
to  the  other,  it  is  clear  that  the  system  of  currents 
would  continue  in  action  :  that  is,  there  would  be  a 
continual  flow  of  oil  in  one  direction  along  the  surface 
of  the  water,  and  of  water  in  the  contrary  direction 
underneath  the  oil. 

Bat  Sir  John  Herschel  maintains  that  no  sach 
effects  as  Maury  describes  could  follow  the  action  .of 
the  sun's  heat  upon  the  equatorial  waters.  He  argues 
thus:  Granting  that  these  waters  become  lighter  and 
expand  in  volume,  yet  they  can  only  move  upward, 
downward,  or  sideways.  There  can  be  nothing  to 
cause  either  of  the  first  two  forms  of  motion ;  and  as 
for  motion  sideways,  it  can  only  result  from  the 
gradual  slope  caused  by  the  bulging  of  the  equatorial 
waters.  He  proceeds  to  show  that  this  slope  is  so 
slight  that  we  cannot  look  upon  it  as  competent  to 
form  any  sensible  current  from  the  equatorial  toward 
the  polar  seas.  And  even  if  it  could,  he  says,  the 
water  thus  flowing  off  would  have  an  eastward  instead 
of  a  westward  motion,  precisely  as  the  counter-trade- 


IS  THE   GULF  STREAM  A  MYTH?  147 

winds,  blowing  from  equatorial  to  polar  regions,  liave 
an  eastward  motion. 

It  is  singular  how  completely  the  supporter  of  each 
rival  view  has  succeeded  in  overthrowing  the  argu- 
ments of  his  opponent.  Certainly  Maury  has  shown 
with  complete  success  that  the  inconstant  trade-winds 
cannot  account  for  the  constant  Gulf  current,  which 
does  not  even  flow  before  them,  but,  in  places,  exactly 
against  their  force.  And  the  reasoning  of  Sir  John 
Herschel  seems  equally  cogent,  for  certainly  the  flow 
of  water  from  equatorial  toward  polar  regions  ought 
from  the  first  to  have  an  eastward,  instead  of  a  west- 
ward motion ;  whereas  the  equatorial  current,  of  which 
the  Gulf  Stream  is  but  the  continuation,  flows  from 
east  to  west,  right  across  the  Atlantic. 

Equally  strange  is  it  to  find  that  each  of  these  emi- 
nent men,  having  read  the  arguments  of  the  other, 
reasserts,  but  does  not  effectually  defend,  his  own 
theory,  and  repeats  with  even  more  damaging  effect 
his  arguments  against  the  rival  view. 

Yet  one  or  other  theory  must  at  least  point  to  the 
true  view,  for  the  Atlantic  is  subject  to  no  other  agen- 
cies which  can  for  a  moment  be  held  to  account  for  a 
phenomenon  of  such  magnificence  as  the  Gulf  Stream. 

It  appears  to  us  that,  on  a  close  examination  of  the 
Gulf-Stream  mechanism,  the  true  mainspring  of  its 
motion  can  be  recognized.  Compelled  to  reject  the 
theory  that  the  trade-winds  generate  tke  equatorial 


148  LIGHT   SCIENCE  FOR  LEISURE   HOURS. 

current  westward,  let  us  consider  whether  Ilerschel's 
arguments  against  the  "  heat-theory  "  may  not  suggest 
a  hint  for  our  guidance.  He  points  out  that  an  over- 
flow from  the  equator  poleward  would  result  in  an 
eastward,  and  not  in  a  westward  current.  This  is 
true.  It  is  equally  true  that  a  flow  of  water  toward 
the  equator  would  result  in  a  westward  current.  But 
no  such  flow  is  observed.  Is  it  possible  that  there  may 
be  such  a  flow,  but  that  it  takes  place  in  a  hidden 
manner?  Clearly  there  may  be.  Sub-marine  currents 
toward  the  equator  would  have  precisely  the  kind 
of  motion  we  require,  and,  if  any  cause  drew  them  to 
the  surface  near  the  equator,  they  would  account  in 
full  for  the  great  equatorial  westward  current. 

At  this  point  we  begin  to  see  that  an  important 
circumstance  has  been  lost  sight  of  in  dealing  with  the 
heat-theory.  The  action  of  the  sun  on  the  surface- 
water  of  the  equatorial  Atlantic  has  only  been  con- 
sidered with  reference  to  its  warming  effects.  But  we 
must  not  forget  that  this  action  has  drying  effects  also. 
It  evaporates  enormous  quantities  of  water,  and  we 
have  to  inquire  whence  the  water  comes  by  which  the 
sea-level  is  maintained.  A  surface-flow  from  the  sub- 
tropical seas  would  suffice  for  this  purpose,  but  no  such 
flow  is  observed.  Whence,  then,  can  the  water  come 
but  from  below  ?  Thus  we  recognize  the  fact  that  a 
process  resembling  suction  is  continually  taking  place 
over  the  wl\ple  area  of  the  equatorial  Atlantic,  the 


IS  THE   GULF  STREAM  A  MYTH?  149 

agent  being  the  intense  lieat  of  the  tropical  sun.  No 
one  can  doubt  that  this  agent  is  one  of  adequate  power. 
Indeed,  the  winds,  conceived  by  Franklin  to  be  the 
primary  cause  of  the  Atlantic  currents,  are  in  reality 
due  to  the  merest  fraction  of  the  energy  inherent  in 
the  sun's  heat. 

"We  have  other  evidence  that  the  indraught  is  from 
below,  in  the  comparative  coldness  of  the  equatorial 
current.  The  Gulf  Stream  is  warm  by  comparison 
with  the  surrounding  waters,  but  the  equatorial  cur- 
rent is  cooler  than  the  tropical  seas.  According  to 
Professor  Ansted,  the  southern  portion  of  the  equa- 
torial current,  as  it  flows  past  Brazil,  "  is  everywhere  a 
cold  current,  generally  from  four  to  six  degrees  below 
the  adjacent  ocean." 

Having  once  detected  the  mainspring  of  the  Gulf- 
Stream  mechanism,  or  rather  of  the  whole  system  of 
oceanic  circulation — for  the  movements  observed  in  the 
Atlantic  have  their  exact  counterpart  in  the  Pacific — 
we  have  no  difficulty  in  accounting  for  all  the  motions 
which  that  mechanism  exhibits.  We  need  no  longer 
look  upon  the  Gulf  Stream  as  the  rebound  of  the 
equatorial  current  from  the  shores  of  North  America. 
Knowing  that  there  is  an  underflow  toward  the 
equator,  we  see  that  there  must  be  a  surface-flow 
toward  the  Poles.  And  this  flow  must  as  inevitably 
result  in  an  easterly  motion,  as  the  underflow  toward 
the  equator  results  in  a  westerly  motion.  "We  have, 


150  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

indeed,  the  phenomena  of  the  trades  and  counter-trades 
exhibited  in  water-currents  instead  of  air-currents. 

(From  S(.  Paul's,  September,  1869.)* 


FLOODS  IN  SWITZERLAND. 


the  past  few  weeks  we  have  witnessed  a  suc- 
cession of  remarkable  evidences  of  Nature's  destructive 
powers.  The  fires  of  Vesuvius,  the  earth-throes  of  the 
sub-equatorial  Andes,  and  the  submarine  disturbance 
which  has  shaken  Hawaii,  have  presented  to  us  the 
various  forms  of  destructive  action  which  the  earth's 
subterranean  forces  can  assume.  In  the  disastrous 
floods  which  have  recently  visited  the  Alpine  cantons 
of  Switzerland,  we  have  evidence  of  the  fact  that 
natural  forces  which  we  are  in  the  habit  of  regarding 
as  beneficent  and  restorative  may  exhibit  themselves 
as  agents  of  the  most  wide-spread  destruction.  "We 
have  pointed  out  elsewhere  (see  p.  249)  how  enormous 
is  the  amount  of  power  of  which  the  rain-cloud  is  the 
representative;  and  in  doing  so  we  have  endeavored 
to  exhibit  the  ^contrast  between  the  steady  action  of 
the  falling  shower  and  the  energy  of  the  processes  of 
which  rain  is  in  reality  the  equivalent.  But  in  the 
floods  which  have  lately  ravaged  Switzerland  we  see 
the  same  facts  illustrated,  not  by  numerical  calcula- 
tions or  by  the  results  of  philosophical  experiments, 

*  See  also  The  Student  for  July,  1868. 


FLOODS  IN  SWITZERLAND.  151 

but  in  action,  and  that  action  taking  place  on  the  most 
widely-extended  scale.  The  whole  of  the  southeastern, 
or,  as  it  may  be  termed,  the  Alpine  half  of  Switzer- 
land, has  suffered  from  these  floods.  If  a  line  be 
drawn  from  the  Lake  of  Constance,  in  the  northeast 
of  Switzerland,  to  the  Col  de  Balme,  in  the  south- 
west, it  will  divide  Switzerland  into  two  nearly  equal 
portions,  and  scarcely  a  canton  within  the  eastern  of 
these  divisions  has  escaped  without  great  damage. 

The  cantons  which  have  suffered  most  terribly  are 
those  of  Tessin,  Orisons,  and  St.  Gall.  The  St. 
Gothard,  Splugen,  and  St.  Bernhardin  routes,  have 
been  rendered  impassable.  Twenty-seven  lives  were 
lost  in  the  St.  Gothard  Pass,  besides  horses  and  wagons 
full  of  merchandise.  It  is  stated  that  on  the  three 
routes  upward  of  eighty  persons  perished.  In  the 
village  of  Loderio  alone,  no  less  than  fifty  deaths  oc- 
curred. So  terrible  a  flood  has  not  taken  place  since 
the  year  1834.  Nor  have  the  cantons  of  Uri  and 
Yalais  escaped.  From  Unterwalden  we  hear  that  the 
heavy  rains  which  took  place  a  fortnight  ago  have 
carried  away  several  large  bridges,  and  many  of  the 
rivers  continue  still  very  swollen.  We  have  already 
described  how  enormous  the  material  losses  are  which 
have  been  caused  by  these  floods.  Many  places  are 
under  water;  others  in  ruins  or  absolutely  destroyed. 
In  Tessin  alone  the  damage  is  estimated  at  forty  thou- 
sand pounds  sterling. 


152  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

A  country  like  Switzerland  must  always  be  liable 
to  the  occurrence,  from  time  to  time,  of  catastrophes 
of  this  sort.  Or  rather,  perhaps,  we  should  draw  a 
distinction  between  the  two  divisions  of  Switzerland 
referred  to  above.  Of  these  the  one  may  be  termed 
the  mountain  half,  and  the  other  the  lake  half  of  the 
country.  It  is  the  former  portion  of  the  country 
which  is  principally  subject  to  the  dynamical  action 
of  water.  A  long-continued  and  heavy  rainfall  over 
the  higher  lands  cannot  fail  to  produce  a  variety  of 
remarkable  effects,  where  the  arrangement  of  moun- 
tains and  passes,  hills,  valleys,  and  ravines,  is  so  com- 
plicated. There  are  places  where  a  large  volume  of 
water  can  accumulate  until  the  barriers  which  have 
opposed  its  passage  to  the  plains  burst  under  its  in- 
creasing weight ;  and  then  follow  those  destructive 
rushes  of  water  which  sweep  away  whole  villages  at 
once.  It  is,  in  fact,  the  capacity  of  the  Swiss  moun- 
tain-region for  damming  up  water,  far  more  than  any 
other  circumstance,  which  renders  the  Swiss  floods  so 
destructive. 

And  then  it  must  be  remembered  that  there  are  at 
all  times  suspended  over  the  plains  and  valleys  which 
lie  beneath  the  Alpine  ranges  enormous  masses  of 
water  in  the  form  of  snow  and  ice.  Although  in  gen- 
eral these  suffer  no  changes  but  those  due  to  the  par- 
tial melting  which  takes  place  in  summer,  and  the  re- 
newed accumulation  which  takes  place  in  winter,  yet 


FLOODS  IN  SWITZERLAND.  153 

when  heavy  rains  fall  upon  the  less  elevated  portions 
of  the  Alpine  snow,  they  not  only  melt  that  snow 
much  more  rapidly  than  the  summer  sun  would  do, 
but  they  wash  down  large  masses,  which  add  largely 
to  the  destructive  power  of  the  descending  waters. 

The  most  destructive  floods  which  have  occurred  in 
Switzerland  have  usually  been  those  which  take  place 
in  early  summer.  The  floods  which  inundated  the 
plains  of  Martigny  in  1818  were  a  remarkable  instance 
of  the  effects  which  result  from  the  natural  damming 
up  of  large  volumes  of  water  in  the  upper  parts  of  the 
Alpine  hill  -  country.  The  whole  of  the  valley  of 
Bagnes,  one  of  the  largest  of  the  lateral  branches  of 
the  main  valley  of  the  Rhone  above  Geneva,  was  con- 
verted into  a  lake,  in  the  spring  of  1818,  by  the  dam- 
ming up  of  a  narrow  pass  into  which  avalanches  of 
snow  and  ice  had  been  precipitated  from  a  lofty  glacier 
overhanging  the  bed  of  the  river  Dranse.  The  icy 
barrier  enclosed  a  lake  no  less  than  half  a  league  in 
length  and  an  eighth  of  a  mile  wide,  and  in  places 
two  hundred  feet  deep.  The  inhabitants  of  the  neigh- 
boring villages  were  terrified  by  the  danger  which  was 
to  be  apprehended  from  the  bursting  of  the  barrier. 
They  cut  a  gallery  seven  hundred  feet  long  through 
the  ice,  while  the  waters  had  as  yet  risen  to  but  a 
moderate  height ;  and  when  the  waters  began  to  flow 
through  this  channel,  its  course  was  deepened  by  the 
melting  of  the  ice,  and  at  length  nearly  half  the  con- 


154  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

tents  of  the  lake  were  safe] y  carried  off.  It  was  hoped 
that  the  process  would  continue,  and  the  country  be 
saved  from  the  danger  which  had  been  so  long  im- 
pending over  it.  But  as  the  heat  of  the  weather  in- 
creased, the  central  part  of  the  barrier  slowly  melted 
away,  until  it  became  too  weak  to  bear  the  enormous 
weight  of  water  which  was  pressing  against  it.  At 
length  it  gave  way,  so  suddenly  and  completely  that 
all  the  water  which  remained  in  the  lake  rushed  out  in 
half  an  hour.  The  downward  passage  of  the  water 
illustrated,  in  a  very  remarkable  way,  the  fact  that  the 
chief  mischief  of  floods  is  occasioned  where  water  is 
checked  in  its  outflow.  For  it  is  related  that,  "  in  the 
course  of  their  descent  the  waters  encountered  several 
narrow  gorges,  and  at  each  of  these  they  rose  to  a 
great  height,  and  then  burst  with  new  violence  into 
the  next  basin,  sweeping  along  forests,  houses,  bridges, 
and  cultivated  land."  Along  the  greater  part  of  its 
course  the  flood  resembled  rather  a  moving  mass  of 
rock  and  mud  than  a  stream  of  water.  Enormous 
masses  of  granite  were  torn  out  of  the  sides  of  the 
valleys  and  whirled  for  hundreds  of  yards  along  the 
course  of  the  flood.  M.  Escher  relates  that  one  of  the 
fragments  thus  swept  along  was  no  less  than  sixty 
yards  in  circumference.  At  first  the  water  rushed 
onward  at  a  rate  of  more  than  a  mile  in  three  minutes, 
and  the  whole  distance  (forty-five  miles)  which  sepa- 
rates the  valley  of  Bagnes  from  the  Lake  of  Geneva 


A   GREAT   TIDAL  WAVE.  155 

was  traversed  in  little  more  than  six  hours.  Tlie 
bodies  of  persons  wlio  had  been  drowned  in  Martigny 
were  found  floating  on  the  farther  side  of  the  Lake  of 
Geneva,  near  Vevey.  Thousands  of  trees  were  torn 
up  by  the  roots,  and  the  ruins  of  buildings  which  had 
been  overthrown  by  the  flood  were  carried  down  be- 
yond Martigny.  In  fact,  the  flood  at  this  point  was 
so  high  that  some  of  the  houses  in  Martigny  "  were 
filled  with  mud  up  to  the  second  story."  Beyond 
Martigny  the  flood  did  but  little  damage,  as  it  here 
expanded  over  the  plain,  and  was  at  once  reduced  in 
depth  and  velocity. 

(From  the  Daily  News  for  October  20,  1868.) 


A  GREAT  TIDAL   WAVE. 

DURING  the  last  few  days  anxious  questionings  have 
been  heard  respecting  the  next  spring  tides.  A  certain 
naval  officer,  who  conceives  that  he  can  trace  in  the 
relative  positions  of  the  sun  and  moon  the  secret  of 
every  important  change  of  weather,  has  described  in. 
the  columns  of  a  contemporary  the  threatening  signifi- 
cance of  the  approaching  conjunction  of  the  sun  and 
moon.  He  predicts  violent  atmospheric  disturbances ; 
though  in  another  place  he  tells  us  merely  that  the 
conjunction  is  to  cause  "  unsettled  weather,"  a  state  of 
matters  to  which  we  in  England  have  become  tolerably 
well  accustomed. 


156  LIGHT   SCIENCE  FOR  LEISURE  HOURS. 

But  people  are  asking  what  is  the  actual  relation 
which  is  to  bring  about  such  terrible  events.  The 
matter  is  very  simple.  On  October  5th,  the  moon  will 
be  new — in  other  words,  if  it  were  not  for  the  bright- 
ness of  the  sun,  we  should  see  the  moon  close  by  that 
luminary  on  the  heavens.  Thus  the  sun  and  moon 
will  pull  with  combined  effect  upon  the  waters  of  the 
earth,  and  so  cause  what  are  called  spring  tides.  This, 
of  course,  happens  at  the  time  of  every  new  moon. 
But  sometimes  the  moon  exerts  a  more  effective  pull 
than  at  other  times  ;  and  the  same  happens  also  in  the 
case  of  the  sun ;  and  on  October  5th,  it  happens  that 
both  the  sun  and  the  moon  will  give  a  particularly 
vigorous  haul  upon  the  earth's  waters.  As  regards 
the  sun,  there  is  nothing  unusual.  Every  October  his 
pull  on  the  ocean  is  much  the  same  as  in  preceding 
Octobers.  But  October  is  a  month  of  high  solar  tides 
— and  for  these  reasons  :  In  September,  as  every  one 
knows,  the  sun  crosses  the  equinoctial;  and  other 
things  being  equal  it  would  be  when  on  the  equinoctial 
that  his  power  to  raise  a  tidal  wave  would  be  greatest. 
But  other  things  are  not  equal ;  for  the  sun  is  not 
always  at  a  fixed  distance  from  the  earth.  He  is 
nearest  in  January ;  so  that  he  would  exert  more 
power  in  that  month  than  in  any  other  if  his  force 
depended  solely  on  distance.  As  matters  actually 
stand,  it  will  be  obvious  that  at  some  time  between 
September  and  January  the  sun's  tidal  power  would 


A   GREAT   TIDAL  WAVE.  157 

have  a  maximum  value.     Thus  it  is  that  October  is  a 
month  of  high  solar  tidal  waves. 

But  is  it  the  lunar  wave  which  will  be  most  effective- 
ly strengthened  at  the  next  spring  tide.  If  we  could 
watch  the  lunar  tidal  wave  alone  (instead  of  always 
finding  it  combined  with  the  solar  wave)  we  should 
find  it  gradually  increasing,  and  then  gradually  dimin- 
ishing, in  a  period  of  about  a  lunar  month.  And  we 
should  find  that  it  was  always  largest  when  the  moon 
looked  largest,  and  vice  versa.  In  other  words,  when 
the  moon  is  in  perigee  the  lunar  wave  is  largest.  But 
then  there  is  another  consideration.  The  lunar  wave 
would  vary  according  to  the  moon's  proximity  to  the 
equinoctial ;  and  (other  things  being  equal)  would  be 
largest  when  .the  moon  is  exactly  opposite  the  earth's 
equator.  If  the  two  effects  are  combined,  that  is,  if 
the  moon  happens  to  be  in  perigee  and  on  the  equi- 
noctial at  the  same  time,  then  of  course  we  get  the 
largest  lunar  tidal  wave  we  can  possibly  have. 

Now,  this  "largest  lunar  wave"  occurs  at  some- 
what long  intervals,  because  the  relation  on  which  it 
depends  is  one  which  is,  so  to  speak,  exceptional. 
Still  the  relation  does  recur,  and  with  a  certain  degree 
of  regularity.  When  it  happens,  however,  it  by  no 
means  follows  that  we  have  a  very  high  tide ;  because 
it  may  occur  when  the  tides  are  near  "neap;"  in 
other  words,  when  the  sun  and  moon  exert  opposing 
effects.  The  largest  lunar  wave  cannot  stand  the 


158  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

drain  which  the  solar  wave  exerts  upon  it  at  the  time 
of  neap  tides.  Nor  would  the  large  lunar  tidal  wave 
produce  an  exceptionally  high  tide,  even  though  it 
were  not  the  time  of  "neap,"  or  were  tolerably  near 
the  time  of  "  spring  "  tides.  Only  when  it  happens 
that  a  large  lunar  wave  combines  fully  with  the  solar 
wave  do  we  get  very  high  tides.  And  when,  in  ad- 
dition to  this  relation,  we  have  the  solar  wave  nearly 
at  a  maximum,  we  get  the  highest  of  all  possible  tides. 
This  is  what  will  happen,  or  all  but  happen,  on  Octobor 
5th  next.  The  combination  of  circumstances  is  almost 
the  most  effective  that  can  possibly  exist. 

But,  after  all,  high  tides  depend  very  importantly 
on  other  considerations  than  astronomical  ones.  Most 
of  us  remember  how  a  predicted  high  tide  some  two 
years  ago  turned  out  to  be  very  moderate,  or,  if  we 
may  use  the  expression,  a  very  "one-horse"  aifair 
indeed,  because  the  winds  had  not  been  consulted,  and 
exerted  their  influence  against  the  astronomers.  A 
long  succession  of  winds  blowing  off-shore  would  re- 
duce a  spring  tide  to  a  height  scarcely  exceeding  the 
ordinary  neap.  On  the  other  hand,  if  we  should  have 
a  long  succession  of  westerly  winds  from  the  Atlantic 
before  the  approaching  high  tide,  it  is  certain  that  a 
large  amount  of  mischief  may  be  done  in  some  of  our 
river-side  regions.* 

As  for  the  predicted  weather  changes,  they  may  bo 
*  The  wave  did  little  mischief. 


A  GREAT  TIDAL  WAVE.  159 

regarded  as  mere  moonshine.  A  number  of  predictions, 
founded  on  the  motions  of  the  sun  and  moon,  have 
found  a  place  during  many  months  past  in  the  columns 
of  a  contemporary;  but  there  has  been  no  greater 
agreement  between  these  predictions  and  the  weather 
actually  experienced  than  any  one  could  trace  between 
Old  More's  weather  prophecies  and  recorded  weather 
changes.  In  other  words,  there '  have  been  certain 
accordances  which  would  be  very  remarkable  indeed 
if  they  did  not  happen  to  be  associated  with  as  many 
equally  remarkable  discordances.  Random  predictions 
would  be  quite  as  satisfactory. 

A  very  amusing  misprint  has  found  its  way  into 
many  newspapers  in  connection  with  the  coming  tide. 
It  is  interesting  as  serving  to  show  how  little  is 
really  known  by  the  general  public  about  some  of  the 
simplest  scientific  matters.  The  original  statement 
announced  that  the  sun  would  not  be  in  perihelion  by 
so  many  seconds  of  semi-diameter,  in  itself  a  very  in- 
correct mode  of  expression.  Still  it  was  clear  that 
what  was  meant  was,  that  the  earth  would  be  so  far 
from  the  place  of  nearest  approach  to  the  sun  that  the 
latter  would  not  look  as.  large  as  it  possibly  can  by 
so  many  seconds  of  semi-diameter.  In  many  papers, 
however,  we  read  that  the  "sun  will  not  be  in  perihe- 
lion by  so  many  seconds  of  mean  chronometer  !  "  "Who 
first  devised  this  marvellous  reading  is  unknown — ho 
should  have  a  statue. 

(From  the  Daily  News  for  September  27,  1869.) 


160  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 


DEEP-SEA  DREDGINGS. 

have  ever  been  strangely  charmed  by  the 
unknown  and  the  seemingly  inaccessible.  The  as- 
tronomer exhibits  the  influence  of  this  charm  as  he 
constructs  larger  and  larger  telescopes,  that  he  may 
penetrate  more  and  more  deeply  beyond  the  veil  which 
conceals  the  greater  part  of  the  universe  from  the 
unaided  eye.  The  geologist  seeking  to  piece  together 
the  fragmentary  records  of  the  past  which  the  earth's 
surface  presents  to  him,  is  equally  influenced  by  the 
charm  of  mystery  and  difficulty.  And  the  microsco- 
pist  who  tries  to  force  from  Nature  the  secret  of  the  infi- 
nitely little,  is  led  on  by  the  same  strange  desire  to 
discover  just  those  matters  which  Nature  has  been  most 
careful  to  conceal  from  us. 

The  energy  with  which  in  recent  times  men  have 
sought  to  master  the  problem  of  deep-sea  sounding 
and  deep-sea  dredging  is,  perhaps,  one  of  the  most 
striking  instances  ever  afforded  of  the  charm  which  the 
unknown  possesses  for  mankind.  Not  long  ago,  one  of 
the  most  eminent  geographers  of  the  sea  spoke  regret- 
fully about  the  small  knowledge  men  have  obtained  of 
the  depths  of  ocean.  "  Greater  difficulties,"  he  re- 
marked, "  than  any  presented  by  the  problem  of  deep- 
sea  research  have  been  overcome  in  other  branches  of 
physical  inquiry.  Astronomers  have  measured  the 


DEEP-SEA  DREDGINGS.  161 

volumes  and  weighed  the  masses  of  the  most  distant 
planets,  and  increased  thereby  the  stock  of  human 
knowledge.  Is  it  creditable  to  the  age  that  the  depths 
of  the  sea  should  remain  in  the  category  of  unsolved 
problems  ?  that  its  6  ooze  and  bottom '  should  be  a 
sealed  volume,  rich  with  ancient  and  eloquent  legends, 
and  suggestive  of  many  an  instructive  lesson  that 
might  be  useful  and  profitable  to  man  ?  " 

Since  that  time,  however,  duep-sea  dredging  has 
gradually  become  rnqre  and  more  thoroughly  under- 
stood and  mastered.  Recently,  when  the  telegraphic 
cable  which  had  lain  so  many  months  at  the  bottom 
of  the  Atlantic  was  hauled  on  board  the  "  Great 
Eastern  "  from  enormous  depths,  men  were  surprised 
and  almost  startled  by  the  narrative.  The  appearance 
of  the  ooze-covered  cable  as  it  was  slowly  raised 
toward  the  surface,  and  the  strange  thrill  which  ran 
through  those  who  saw  it  and  remembered  through 
what  mysterious  depths  it  had  twice  passed ;  its  break- 
ing away  almost  from  the  very  hands  of  those  who 
sought  to  draw  it  on  board ;  and  the  successful  re- 
newal of  the  attempt  to  recover  the  cable — all  these 
things  were  heard  of  as  one  listens  to  a  half-incredible 
tale.  Yet  when  that  work  was  accomplished  deep-sea 
dredging  had  already  been  some  time  a  science,  and 
many  things  had  been  achieved  by  its  professors  which 
presented,  in  reality,  greater  practical  difficulties  than 
the  recovery  of  the  Atlantic  Cable. 


162  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

Recently,  however,  deep-sea  researches  have  been 
carried  on  with  results  which  are  even  more  sensa- 
tional, so  to  speak,  than  the  grappling  feat  which  so 
surprised  us.  Seas  so  deep  that  many  of  the  loftiest 
summits  of  the  Alps  might  be  completely  buried  be- 
neath them  have  been  explored.  Dredges  weighing 
with  their  load  of  mud  nearly  half  a  ton  have  been 
hauled  up  without  a  hitch  from  depths  of  some  14,000 
feet.  But  not  merely  has  comparatively  rough  work 
of  this  sort  been  achieved,  but  by^a  variety  of  ingenious 
contrivances  men  of  science  have  been  able  to  measure 
the  temperature  of  the  sea  at  depths  where  the  press- 
ure is  so  enormous  as  to  be  equivalent  to  a  weight  of 
more  than  430  tons  on  every  square  foot  ot  surface. 

The  results  of  these  researches  are  even  more  re- 
markable and  surprising,  however,  than  the  means  by 
which  they  have  been  obtained.  S-ir  Charles  Lyell 
has  fairly  spoken  of  them  as  so  astonishing  "  that  they 
have  to  the  geologist  almost  a  revolutionary  character." 
Let  us  consider  a  few  of  them. 

]STo  light  can  be  supposed  to  penetrate  to  the  enor- 
mous depths  just  spoken  of.  Therefore,  how  certainly 
we  might  conclude  that  there  can  be  no  life  there  !  If, 
instead  of  dealing  with  the  habitability  of  planets, 
Whewell,  in  his  "  Plurality  of  Worlds,"  had  been 
considering  the  question  whether  at  depths  of  two  or 
three  miles  living  creatures  could  subsist,  how  con- 
vincingly would  he  have  proved  the  absurdity  of  such 


DEEP-SEA  DREDGINGS.  163 

a  supposition !  Intense  cold,  perfect  darkness,  and  a 
persistent  pressure  of  two  or  three  tons  to  the  square 
inch — such,  he  might  have  argued,  are  the  con- 
ditions under  which  life  exists,  if  at  all,  in  those 
dismal  depths.  And  even  if  he  had  been  disposed  to 
concede  the  bare  possibility  that  life  of  some  sort  may 
be  found  there,  then  certainly  he  would  have  urged, 
some  new  sense  must  replace  sight — the  creatures  in 
these  depths  can  assuredly  have  no  eyes,  or  onty  rudi- 
mentary ones. 

But  the  recent  deep  sea-dredgings  have  proved  that 
not  only  does  life  exist  'in  the  very  deepest  parts  of 
the  Atlantic,  but  that  the  beings  which  live  and  move 
and  have  their  being  beneath  the  three-mile  mountain 
of  water  have  eyes  which  the  ablest  naturalists  pro- 
nounce to  be  perfectly  developed.  Light,  then,  of 
some  sort  must  exist  in  those  abysms,  though  whether 
the  home  of  the  deep-sea  animals  be  phosphorescent, 
as  Sir  Charles  Lyell  suggests,  or  how  light  may  reach 
these  creatures,  we  have  no  present  means  of  deter- 
mining. 

If  there  is  one  theory  which  geologists  have 
thought  more  justly  founded  than  all  others,  it  is  the 
view  that  the  various  strata  of  the  earth  were  formed 
at  different  times.  A  chalk  district,  for  example,  lying 
side  by  side  with  a  sandstone  district,  has  been  referred 
to  a  totally  different  era.  Whether  the  chalk  was 
formed  first,  or  whether  the  sandstone  existed  before 


164  LIGHT   SCIENCE   FOR  LEISURE  HOURS. 

the  minute  races  came  into  being  which  formed  the 
cretaceous  stratum,  might  be  a  question.  But  no 
doubt  existed  in  the  minds  of  geologists  that  each 
formation  belonged  to  a  distinct  period.  Now,  how- 
ever, Dr.  Carpenter  and  Professor  Thomson  may 
fairly  say,  "  We  have  changed,  all  this."  It  has 
been  found  that  at  points  of  the  sea-bottom  only  eight 
or  ten  miles  apart,  there  may  be  in  progress  the 
formati6n  of  a  cretaceous  deposit  and  of  a  sandstone 
region,  each  with  its  own  proper  fauna.  "  Wherever 
similar  conditions  are  found  upon  the  dry  land  of  the 
present  day,"  remarks  Dr.  Carpenter,  "it  has  been 
supposed  that  the  formation  of  chalk  and  the  for- 
mation of  sandstone  must  have  been  separated  from 
each  other  by  long  periods,  and  the  discovery  that 
they  may  actually  coexist  upon  adjacent  surfaces  has 
done  no  less  than  strike  at  the  very  root  of  the 
customary  assumptions  with  regard  to  geological 
time."  * 

Even  more  interesting,  perhaps,  to  many,  are  the 
results  which  have  been  obtained  respecting  the  vary- 
ing temperatures  of  deep-sea  regions.  The  peculiarity 
just  considered  is,  indeed,  a  consequence  of  such  varia- 
tions ;  but  the  fact  itself  is  at  least  as  interesting  as 
the  consequences  which  flow  from  it.  It  throws  light 

*  This  opinion  Dr.  Carpenter  has  since  somewhat  modified.  It  will 
be  remembered,  of  course,  that  the  evidence  derived  from  the  nature  of 
superposed  strata  is  in  no  way  affected  by  what  is  shown  above  to  hold 
sis  respects  adjacent  deposits. 


DEEP-SEA  DREDGIXGS.  105 

on  the  long-standing  controversy  respecting  the  oceanic 
circulation.  It  has  been  found  that  the  depths  of  the 
equatorial  and  tropical  seas  are  colder  than  those  of  the 
North  Atlantic.  In  the  tropics  the  deep-sea  tempera- 
ture is  considerably  below  the  freezing-point  of  fresh 
water ;  in  the  deepest  part  of  the  Bay  of  Biscay  the 
temperature  is  several  degrees  above  the  freezing-point. 
Thus  one  learns  that  the  greater  part  of  the  water 
which  lies  deep  below  the  surface  of  the  equatorial  and 
tropical  seas  comes  from  the  Antarctic  regions,  though 
undoubtedly  there  are  certain  relatively  narrow 
currents  which  carry  the  waters  of  the  Arctic  seas  to 
the  tropics.  The  great  point  to  notice  is  that  the 
water  under  the  equatorial  seas  must  really  have 
travelled  from  polar  regions.  A  cold  of  30°  can  be 
explained  in  no  other  way.  "We  see  at  once,  therefore, 
the  explanation  of  those  westerly  equatorial  currents 
which  have  been  so  long  a  subject  of  contest.  Sir 
John  Herschel  failed  to  prove  that  they  are  due  to  the 
trade-winds,  but  Maury  failed  equally  to  prove  that 
they  are  due  to  the  great  warmth  and  consequent 
buoyancy  of  the  equatorial  waters.  In  fact,  while 
Maury  showed  very  convincingly  that  the  great  system 
of  oceanic  circulation  is  carried  on  despite  the  winds, 
Herschel  proved  in  an  equally  convincing  manner  that 
the  overflow  conceived  by  Maury  should  result  in  an 
easterly  instead  of  a  westerly  current.  Recently  the 
theory  was  put  forward  that  the  continual  process  of 


1G6  LIGHT   SCIENCE  FOR  LEISUltE  HOURS. 

evaporation  going" on  in  the  equatorial  regions  leads  to 
an  indraught  of  cold  water  in  bottom-currents  from 
the  polar  seas.  Such  currents  coming  toward  the 
equator,  that  is,  travelling  from  latitudes  where  the 
earth's  eastwardly  motion  is  less  to  latitudes  in  which 
that  motion  is  greater,  would  lag  behind,  that  is,  would 
have  a  westwardly  motion.  It  seems  now  placed 
beyond  a  doubt  that  this  is  the  true  explanation  of  the 
equatorial  ocean-currents. 

Such  are  a  few,  and  but  a  few,  among  the  many 
interesting  results  which  have  followed  from  the  recent 
researches  of  Dr.  Carpenter  and  Professor  Thomson 
into  the  hitherto  little  known  depths  of  the  great  sea. 

(From  the  Spectator,  December  4,  1869.) 


THE  TUNNEL  THROUGH  MONT  CENTS. 

MEX  flash  their  messages  across  mighty  continents 
and  'beneath  the  bosom  of  the  wide  Atlantic;  they 
weigh  the  distant  planets,  and  analyze  the  sun  and  the 
stars ;  they  span  Niagara  with  a  railway  bridge,  and 
pierce  the  Alps  with  a  railway  tunnel :  yet  the  poet  of 
the  age  in  which  all  these  things  are  done  or  doing 
sings,  u~We  men  are  a  puny  race."  And  certainly, 
the  great  works  which  belong  to  man  as  a  race  can  no 
more  be  held  to  evidence  the  importance  of  the  indi- 
vidual man  than  the  vast  coral  reefs  and  atolls  of  the 


THE  TUNNEL  THROUGH  MONT   CENTS.  167 

Pacific  can  be  held  to  evidence  the  working-power  of 
the  individual  coral  polype.  But  if  man,  standing 
alone,  is  weak,  man  working  according  to  the  law 
assigned  to  his  race  from  the  beginning — that  is,  in 
fellowship  with  his  kind — is  verily  a  being  of  power. 

Perhaps  no  work  ever  undertaken  by  men  strikes 
one  as  more  daring  than  the  attempt  to  pierce  the  Alps 
with  a  tunnel.  Nature  seems  to  have  upreared  these 
mighty  barriers  as  if  with  the  design  of  showing  man 
how  weak  he  is  in  her  presence.  Even  the  armies  of 
Hannibal  and  Napoleon  seemed  all  but  powerless  in 
the  face  of  these  vast  natural  fastnesses.  Compelled 
to  creep  slowly  and  cautiously  along  the  difficult  and 
narrow  ways  which  alone  were  open  to  them,  decimated 
by  the  chilling  blasts  which  swept  the  face  of  the  rug- 
ged mountain-range,  and  dreading  at  every  moment 
the  pitiless  swoop  of  the  avalanche,  the  French  and 
Carthaginian  troops  exhibited  little  of  the  pomp  and 
dignity  which  we  are  apt  to  associate  with  the  opera- 
tions of  warlike  armies.  Had  the  denizen  of  some 
other  planet  been  able  to  watch  their  progress,  he  might 
indeed  have  said,  "  These  men  are  a  puny  race."  In  this 
only,  that  they  succeeded,  did  the  troops  of  Hannibal 
and  Napoleon  assert  the  dignity  of  the  human  race. 
Grand  as  was  the  aspect  of  Nature,  and  mean  as  was 
that  of  man  during  the  progress  of  the  contest,  it  was 
Nature  that  was  conquered — man  that  overcame.  And 
now  man  has  entered  on  a  new  conflict  with  Nature  in 


168  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

the  gloomy  fastnesses  of  the  Alps.  The  barrier  which 
he  had  scaled  of  old  he  has  now  undertaken  to  pierce. 
And  the  work — bold  and  daring  as  it  seems — is  three 
parts  finished. 

The  Mont  Cenis  tunnel  was  sanctioned  by  the  Sar- 
dinian Government  in  1857,  and  arrangements  were 
made  for  fixing  the  perforating  machinery  in  the  years 
1858  and  1859.  But  the  wrork  was  not  actually  com- 
menced until  November,  1860.  The  tunnel,  which 
will  be  fully  seven  and  a  half  miles  in  length,  was  to 
be  completed  in  twenty-five  years.  The  entrance  to 
the  tunnel  on  the  side  of  France  is  near  the  little  village 
of  Fourneau,  and  lies  3,946  feet  above  the  level  of  the 
sea.  The  entrance  on  the  side  of  Italy  is  in  a  deep 
valley  at  Bardoneche,  and  lies  4,380  feet  above  the  sea- 
level.  Thus  there  is  a  difference  of  level  of  434  feet. 
But  the  tunnel  will  actually  rise  445  feet  above  the 
level  of  the  French  end,  attaining  this  height  at  a. dis- 
tance of  about  four  miles  from  that  extremity ;  in  the 
remaining  three  and  three-quarter  miles  there  will  be 
a  fall  of  only  ten  feet,  so  that  this  part  of  the  line  will 
be  practically  level. 

The  rocks  through  which  the  excavations  have  been 
made  have  been  for  the  most  part  very  difficult  to  work. 
Those  who  imagine  that  the  great  mass  of  our  moun- 
tain-ranges consists  of  such  granite  as  is  made  use  of  in 
our  buildings,  and  is  uniform  in  texture  and  hardness, 
greatly  underrate  the  difficulties  with  which  the  engi- 


THE   TUNNEL  THROUGH  MONT   CENIS.  169 

neers  of  this  gigantic  work  have  had  to  contend.  A 
large  part  of  the  rock  consists  of  a  crystallized  cal- 
careous schist,  much  broken  and  contorted;  and 
through  this  rock  run  in  every  direction  large  masses 
of  pure  quartz.  It  will  be  conceived  how  difficult  the 
work  has  been  of  piercing  through  so  diversified  a  siib- 
stance  as  this.  The  perforating  machines  are  calculated 
to  work  best  when  the  resistance  is  uniform ;  and  it 
has  often  happened  that  the  unequal  resistance  offered 
to  the  perforators  has  resulted  in  injury  to  the  chisels. 
But  before  the  work  of  perforating  began,  enormous 
difficulties  had  to  be  contended  with.  It  will  be  un- 
derstood that,  in  a  tunnel  of  such  vast  length,  it  was 
absolutely  necessary  that  the  perforating  processes 
carried  on  from  the  two  ends  should  be  directed  with 
the  most  perfect  accuracy.  It  has  often  happened  in 
short  tunnels  that  a  want  of  perfect  coincidence  has 
existed  between  the  two  halves  of  the  work,  and  the  tun- 
nellers  from  one  end  have  sometimes  altogether  failed 
to  meet  those  from  the  other.  But  in  a  short  tunnel 
this  want  of  coincidence  is  not  very  important,  because 
the  two  interior  ends  of  the  tunnellings  cannot  in  any 
case  be  far  removed  from  each  other.  But  in  the  case 
of  the  Mont  Cenis  tunnel  any  inaccuracy  in  the  direc- 
tion of  the  two  tunnellings  would  have  been  fatal  to 
the  success  of  the  work,  since  when  the  two  ought  to 
meet  it  might  be  found  that  they  were  laterally  sepa- 
rated by  two  or  three  hundred  yards.  Hence  it  was 


170  LIGHT   SCIENCE  FOR  LEISURE  HOURS. 

necessary,  before  the  work  began,  to  survey  the  interme- 
diate country,  so  as  to  ascertain  with  the  most  perfect 
accuracy  the  bearings  of  one  end  of  the  tunnel  from 
the  other.  "  It  was  necessary,"  says  the  narrative  of 
these  initial  labors,  "to  prepare  accurate  plans  and 
sections  for  the  determination  of  the  levels,  to  fix  the 
axis  of  the  tunnel,  and  to  '  set  it  out '  on  the  mountain- 
top  ;  to  erect  observatories  and  guiding-signals,  solid, 
substantial,  and  true."  When  we  remember  the  na- 
ture of  the  passes  over  the  Cenis,  we  can  conceive 
the  difficulty  of  setting  out  a  line  of  this  sort  over  the 
Alpine  range.  The  necessity  of  continually  climbing 
over  rocks,  ravines,  and  precipices  in  passing  from 
station  to  station  involved  difficulties  which,  great  as 
they  were,  were  as  nothing  when  compared  with  the 
difficulties  resulting  from  the  bitter  weather  experi- 
enced on  those  rugged  mountain-heights.  The  tem- 
pests which  sweep  the  Alpine  passes — the  ever-recur- 
ing  storms  of  rain,  sleet,  and  driving  snow,  are  trying 
to  the  ordinary  traveller.  It  will  be  understood,  there- 
fore, how  terribly  they  must  have  interfered  with  the 
delicate  processes  involved  in  surveying.  It  often 
happened  that  for  days  together  no  work  of  any  sort 
could  be  done  owing  to  the  impossibility  of  using  levels 
and  theodolites  when  exposed  to  the  stormy  weather 
and  bitter  cold  of  these  lofty  passes.  At  length,  how- 
ever, the  work  was  completed,  and  that  with  such 
success  that  the  greatest  deviation  from  exactitude  was 


TORNADOES.  171 

Aess  than  a  single  foot  for  the  whole  length  of  the  seven 
and  a  half  miles. 

Equally  remarkable  and  extensive  were  the  labors 
connected  with  the  preparatory  works.  New  and  solid 
roads,  bridges,  canals,  magazines,  workshops,  forges, 
furnaces,  and  machinery,  had  to  be  constructed ;  resi- 
dences had  to  be  built  for  the  men,  and  offices  for  the 
engineers ;  in  fact,  at  each  extremity  of  the  tunnel  a 
complete  establishment  had  to  be  formed.  Those  who 
have  traversed  Mont  Cenis  since  the  works  began  have 
been  perplexed  by  the  strange  appearance  and  charac- 
ter of  the  machinery  and  establishments  to  be  seen  at 
Modane  and  Fourneau.  The  mass  of  pipes  and  tubes, 
tanks,  reservoirs,  and'machinery,  which  would  be  mar- 
vellous anywhere,  has  a  still  stranger  look  in  a  wild 
and  rugged  Alpine  pass. 

(From  the  Daily  News.) 


TORNADOES. 

THE  inhabitants  of  the  earth  are  subjected  to  agen- 
cies which — beneficial  doubtless  in  the  long-run,  perhaps 
necessary  to  the  very  existence  of  terrestrial  races — 
appear,  at  first  sight,  energetically  destructive.  Such 
are — in  order  of  destructiveness — the  hurricane,  the 
earthquake,  the  volcano,  and  the  thunder-storm.  "When 
we  read  of  earthquakes  such  as  those  which  overthrew 
Lisbon,  Callao,  and  Riobamba,  and  learn  that  one 


172  LIGHT   SCIENCE  FOR  LEISURE  HOURS. 

hundred  thousand  persons  fell  victims  in  the  great 
Sicilian  earthquake  in  1693,  and  probably  three  hun- 
dred thousand  in  the  two  earthquakes  which  assailed 
Antioch  in  the  years  526  and  612,  we  are  disposed  to 
assign  at  once  to  this  devasting  phenomenon  the  fore- 
most place  among  the  agents  of  destruction.  But  this 
judgment  must  be  reversed  when  we  consider  that 
earthquakes — though  so  fearfully  and  suddenly  destruc- 
tive both  to  life  and  property — yet  occur  but  seldom 
compared  with  wind-storms,  while  the  eifects  of  a 
real  hurricane  are  scarcely  less  destructive  than  those 
of  the  sharpest  shocks  of  earthquake.  After  ordinary 
storms  long  miles  of  the  sea-coast  are  strewn  with  the 
wrecks  of  many  once  gallant  ships,  and  with  the  bodies 
of  their  hapless  crews.  In  the  spring  of  1866  there 
might  be  seen  at  a  single  view  from  the  heights  near 
Plymouth  twenty-two  shipwrecked  vessels,  and  this 
after  a  storm,  which,  though  severe,  was  but  trifling 
compared  with  the  hurricanes  which  sweep  over  the 
torrid  zones,  and  thence — scarcely  diminished  in  force — 
as  far  north  sometimes  as  our  own  latitudes.  It  was 
in  such  a  hurricane  that  the  "Royal  Charter"  was 
wrecked,  and  hundreds  of  stout  ships  with  her.  In  the 
great  hurricane  of  1T80,  which  commenced  at  Barba- 
does  and  swept  across  the  whole  breadth  of  the  North 
Atlantic,  fifty  sail  were  driven  ashore  at  the  Bermudas, 
two  line-of-battle  ships  went  down  at  sea,  and  upward 
of  twenty  thousand  persons  lost  their  lives  on  the 


TORNADOES.  173 

land.  So  tremendous  was  the  force  of  this  hurricane 
(Captain  Maury  tells  us)  that  "  the  bark  was  blown 
from  the  trees,  and  the  fruits  of  the  earth  destroyed ; 
the  very  bottom  and  depths  of  the  sea  were  uprooted 
— forts  and  castles  were  washed  away,  and  their  great 
guns  carried  in  the  air  like  chaif ;  houses  were  razed ; 
ships  wrecked;  and  the  bodies  of  men  and  beasts 
lifted  up  in  the  air  and  dashed  to  pieces  in  the  storm  " 
— an  account,  however,  which  (though  doubtless 
faithfully  rendered  by  Maury  from  the  authorities  he 
consulted)  must  perhaps  be  accepted  cum  grano,  and 
especially  with  reference  to  the  great  guns  carried  in 
the  air  "like  chaff."* 

In  the  gale  of  August,  1782,  all  the  trophies  of 
Lord  Rodney's  victory,  except  the  "  Ardent,"  were  de- 
stroyed, two  British  ships-of-the-line  foundered  at  sea, 
numbers  of  merchantmen  under  Admiral  Graves's  con- 
voy were  wrecked,  and  at  sea  alone  three  thousand 
lives  were  lost. 

Bat  quite  recently  a  storm  far  more  destructive 
than  these  swept  over  the  Bay  of  Bengal.  Most  of  our 
readers  doubtless  remember  the  great  gale  of  October, 
1864,  in  which  all  the  ships  in  harbor  at  Calcutta 
were  swept  from  their  anchorage,  and  driven  one  upon 
another  in  inextricable  confusion.  Fearful  as  was  the 

*  We  remember  to  have  read  that  in  this  hurricane  guns  which  had 
long  lain  under  water  were  washed  up  like  mere  drift  upon  the  beach. 
Perhaps  this  circumstance  grew  gradually  into  the  incredible  story 
above  recorded. 


174  LIGHT   SCIENCE  FOR  LEISURE  HOURS. 

loss  of  life  and  property  in  Calcutta  harbor,  the  de- 
struction on  land  was  greater.  A  vast  wave  swept 
for  miles  over  the  surrounding  country,  embankments 
were  destroyed,  and  whole  villages,  with  their  inhab- 
itants, were  swept  away.  Fifty  thousand  souls,  it  is 
believed,  perished  in  this  fearful  hurricane. 

The  gale  which  has  just  ravaged  the  Gulf  of  Mexi- 
co adds  another  to  the  long  list  of  disastrous  hurri- 
canes. As  we  write,  the  effects  produced  by  this 
tornado  are  beginning  to  be  made  known.  Already 
its  destructiveness  has  become  but  too  certainly  evi- 
denced. 

The  laws  which  appear  to  regulate  the  generation 
and  the  progress  of  cyclonic  storms  are  well  worthy 
of  careful  study. 

The  regions  chiefly  infested  by  hurricanes  are  the 
West  Indies,  the  southern  parts  of  the  Indian  Ocean, 
the  Bay  of  Bengal,  and  the  China  Seas.  Each  region 
has  its  special  hurricane  season. 

In  the  West  Indies,  cyclones  occur  principally  in 
August  and  September,  when  the  southeast  monsoons 
are  at  their  height.  At  the  same  season  the  African 
southwesterly  monsoons  are  blowing.  Accordingly, 
there  are  two  sets  of  winds,  both  blowing  heavily  and 
steadily  from  the  Atlantic,  disturbing  the  atmospheric 
equilibrium,  and  thus  in  all  probability  generating  the 
great  West-Indian  hurricanes.  The  storms  thus  aris- 
ing show  their  force  first  at  a  distance  of  about  six  or 


TORNADOES.  175 

seven  hundred  miles  from  the  equator,  and  far  to  the 
east  of  the  region  in  which  they  attain  their  greatest 
fnry.  They  sweep  with  a  northwesterly  course  to  the 
Gulf  of  Mexico,  pass  thence  northward,  and  so  to  the 
northeast,  sweeping  in  a  wide  curve  (resembling  the 
letter  U  placed  thus  CH)  around  the  "West-Indian  seas, 
and  thence  travelling  across  the  Atlantic,  generally 
expending  their  fury  before  they  reach  the  shores  of 
Western  Europe.  This  course  is  the  storm-track  (or 
storm-  c^  as  we  shall  call  it).  Of  the  behavior  of  the 
winds  as  they  traverse  this  track,  we  shall  have  to 
speak  when  we  come  to  consider  the  peculiarity  from 
which  these  storms  derive  their  names  of  "  cyclones" 
and  "  tornadoes." 

The  hurricanes  of  the  Indian  Ocean  occur  at  the 
"  changing  of  the  monsoons."  "  During  the  interreg- 
num," writes  Maury,  "  the  fiends  of  the  storm  hold 
their  terrific  sway."  Becalmed  often  for  a  day  or  two, 
seamen  hear  moaning  sounds  in  the  air,  forewarning 
them  of  the  coming  storm.  Then,  suddenly,  the  winds 
break  loose  from  the  forces  which  have  for  a  while  con- 
trolled them,  and  "  seem  to  rage  with  a  fury  that 
would  break  up  the  fountains  of  the  deep." 

In  the  North  Indian  seas  hurricanes  rage  at  the 
same  season  as  in  the  West  Indies. 

In  the  China  seas  occur  those  fearful  gales  known 
among  sailors  as  "  typhoons,"  or  "  white  squalls." 
These  take  place  at  the  changing  of  the  monsoons. 


176  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

Generated,  like  the  West-Indian  hurricanes,  at  a  dis- 
tance of  some  ten  or  twelve  degrees  from  the  equator, 
typhoons  sweep — in  a  curve  similar  to  that  followed 
by  the  Atlantic  storms  —  around  the  East  -  Indian 
Archipelago,  and  the  shores  of  China  to  the  Japanese 
Islands. 

There  occur  land-storms,  also,  of  a  cyclonic  charac- 
ter in  the  valley  of  the  Mississippi.  "  I  have  often  ob- 
served the  paths  of  such  storms,"  says  Maury,  "  through 
the  forests  of  the  Mississippi.  There  the  track  of 
these  tornadoes  is  called  a  '  wind-road,'  because  they 
make  an  avenue  through  the  wood  straight  along,  and 
as  clear  of  trees  as  if  the  old  denizens  of  the  forest  had 
been  cleared  with  an  axe.  I  have  seen  trees  three  or 
four  feet  in  diameter  torn  up  by  the  roots,  and  the  top, 
with  its  limbs,  lying  next  the  hole  whence  the  root 
came."  Another  writer,  who  was  an  eye-witness  to 
the  progress  of  one  of  these  American  land-storms, 
thus  speaks  of  its  destructive  effects  :  "  I  saw,  to  my 
great  astonishment,  that  the  noblest  trees  of  the  forest 
were  falling  into  pieces.  A  mass  of  branches,  twigs, 
foliage,  and  dust,  moved  through  the  air,  whirled  on- 
ward like  a  cloud  of  feathers,  and  passing,  disclosed 
a  wide  space  filled  with  broken  trees,  naked  stumps, 
and  heaps  of  shapeless  ruins,  which  marked  the  path 
of  the  tempest." 

If  it  appeared,  on  a  careful  comparison  of  observa- 
tions made  in  different  places,  that  these  winds  swept 


TORNADOES.  177 

directly  along  those  tracks  wliich  they  appear  to  fol- 
low, a  comparatively  simple  problem  would  be  pre- 
sented to  the  meteorologist.  But  this  is  not  found  to 
be  the  case.  At  one  part  of  a  hurricane's  course  the 
storm  appears  to  be  travelling  with  fearful  fury  along 
the  true  storm-  c{  •  at  another  less  furiously  directly 
across  the  storm  -  track ;  at  another,  but  with  yet 
diminished  force,  though  still  fiercely,  in  a  direction 
exactly  opposite  to  that  of  the  storm-track. 

All  these  motions  appear  to  be  fairly  accounted  for 
by  the  theory  that  the  true  path  of  the  storm  is  a 
spiral— or  rather,  that  while  the  centre  of  disturbance 
continually  travels  onward  in  a  widely-extended  curve, 
the  storm-wind  sweeps  continually  around  the  centre 
of  disturbance,  as  a  whirlpool  around  its  vortex. 

And  here  a  remarkable  circumstance  attracts  our 
notice,  the  consideration  of  which  points  to  the  mode 
in  which  cyclones  may  be  conceived  to  be  generated. 
It  is  found,  by  a  careful  study  of  different  observations 
made  upon  the  same  storm,  that  cyclones  in  the 
northern  hemisphere  invariably  sweep  round  the  on- 
ward travelling  vortex  of  disturbance  in  one  direction, 
and  southern  cyclones  in  the  contrary  direction.  If 
we  place  a  watch,  face  upward,  upon  one  of  the 
northern  cyclone  regions  in  a  Mercator's  chart,  then 
the  motion  of  the  hands  is  contrary  to  the  direction  in 
which  the  cyclone  whirls ;  when  the  watch  is  shifted 
to  a  southern  cyclone  region,  the  motion  of  the  hands 


178  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

takes  place  in  the  same  direction  as  the  cyclone  mo- 
tion. This  peculiarity  is  converted  into  the  following 
rule-of-thumb  for  sailors  who  encounter  a  cyclone,  and 
seek  to  escape  from  the  region  of  fiercest  storm : 
Facing  the  wind,  the  centre  or  vortex  of  the  storm  lies 
to  the  right  in  the  northern,  to  the  left  in  the  southern, 
hemisphere.  Safety  lies  in  flying  from  the  centre  in 
every  case  save  one — that  is,  when  the  sailor  lies  in 
the  direct  track  of  the  advancing  vortex.  In  this 
case,  to  fly  from  the  centre  would  be  to  keep  in  the 
storm-track ;  the  proper  course  for  the  sailor  when 
thus  situated  is  to  steer  for  the  calmer  side  of  the 
storm-track.  This  is  always  the  outside  of  the  cj,  as 
will  appear  from  a  moment's  consideration  of  the  spiral 
curve  traced  out  by  a  cyclone.  Thus,  if  the  seaman 
scud  before  the  wind — in  all  other  cases  a  dangerous 
expedient  in  a  cyclone  * — he  will  probably  escape  un- 
scathed. There  is,  however,  this  danger,  that  the 
storm-track  may  extend  to  or  even  slightly  overlap 
the  land,  in  which  case  scudding  before  the  gale  would 
bring  the  ship  upon  a  lee-shore.  And  in  this  way 
many  gallant  ships  have,  doubtless,  suffered  wreck. 

The  danger  of  the  sailor  is  obviously  greater,  how- 
ever, when  he  is  overtaken  by  the  storm  on  the  inner 
side  of  the  storm-  et  Here  he  has  to  encounter  the 

*  A  ship  by  scudding  before  the  gale  may — if  the  captain  is  not 
familiar  with  the  laws  of  cyclones — go  round  and  round  without  escap- 
ing. The  ship  "Charles  Heddlc"  did  this  in  the  East  Indies,  going 
round  no  less  than  five  times. 


TORNADOES.  179 

double  force  of  tlie  cyclonic  whirl  and  of  the  advan- 
cing storm-system,  instead  of  the  difference  of  the  two 
motions,  as  on  the  outer  side  of  the  storm-track.  His 
chance  of  escape  will  depend  on  his  distance  from  the 
central  path  of  the  cyclone.  If  near  to  this,  it  is 
equally  dangerous  for  him  to  attempt  to  scud  to  the 
safer  side  of  the  track,  or  to  beat  against  the  wind  by 
the  shorter  course  which  would  lead  him  out  of  the 
storm  -cj  on  its  inner  side.  It  has  been  shown  by 
Colonel  Sir  W.  Reid  that  this  is  the  quarter  in  which 
vessels  have  been  most  frequently  lost. 

But  even  the  danger  of  this  most  dangerous  quar- 
ter admits  of  degrees.  It  is  greatest  where  the  storm 
is  sweeping  round  the  most  curved  part  of  its  track, 
\vhich  happens  in  about  latitude  twenty-five  or  thirty 
degrees.  In  this  case,  a  ship  may  pass  twice  through 
the  vortex  of  the  storm.  Here  hurricanes  have  worked 
their  most  destructive  effects.  And  thus  it  happens 
that  sailors  dread,  most  of  all,  the  part  of  the  Atlantic 
near  Florida  and  the  Bahamas,  and  the  region  of  the 
Indian  Ocean  which  lies  south  of  Bourbon  and  Mau- 
ritius. 

To  show  how  important  it  is  that  captains  should 
understand  the  theory  of  cyclones  in  both  hemispheres, 
we  shall  her$  relate  the  manner  in  which  Captain  J". 
V.  Hall  escaped  from  a  typhoon  of  the  China  seas. 
About  noon,  when  three  days  out  from  Macao,  Cap- 
tain Hall  saw  a  a  most  wild  and  uncommon-looking 


180  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

halo  round  the  sun."  On  the  afternoon  of  the  next 
day,  the  barometer  had  commenced  to  fall  rapidly; 
and  though,  as  yet,  the  weather  was  fine,  orders  were 
at  once  given  to  prepare  for  a  heavy  gale.  Toward 
evening,  a  bank  of  cloud  was  seen  in  the  southeast, 
but  when  night  closed,  the  weather  was  still  calm  and 
the  water  smooth,  though  the  sky  looked  wild  and  a 
scud  was  coining  on  from  the  northeast.  "  I  was 
much  interested,"  says  Captain  Hall,  "  in  watching 
for  the  commencement  of  the  gale,  which  I  now  felt 
sure  was  coming.  That  bank  to  the  southeast  was  the 
meteor  (cyclone)  approaching  us,  the  northeast  scud 
the  outer  northwest  portion  of  it ;  and  when  at  night 
a  strong  gale  came  on  about  north,  or  north-north- 
west, I  felt  certain  we  were  on  its  western  and  south- 
western verge.  It  rapidly  increased  in  violence ;  but 
I  was  pleased  to  see  the  wind  veering  to  the  north- 
west, as  it  convinced  me  that  I  had  put  the  ship  on 
the  right  track,  namely,  on  the  starboard  tack,  stand- 
ing, of  course,  to  the  southwest.  From  ten  A.  M.  to 
three  P.  M.  it  blew  with  great  violence,  but  the  ship 
being  well  prepared  rode  comparatively  easy.  The 
barometer  was  now  very  low,  the  centre  of  the  storm 
passing  to  the  northward  of  us,  to  which  we  might 
have  been  very  near  had  we  in  the  first  place  put  the 
ship  on  the  larboard  tack." 

But  the  most  remarkable  point  of  Captain  Hall's 
account  remains  to  be  mentioned.     He  had  gone  out 


TORNADOES.  181 

of  his  course  to  avoid  the  storm,  but  when  the  wind 
fell  to  a  moderate  gale  he  thought  it  a  pity  to  lie  so  far 
from  his  proper  course,  and  made  sail  to  the  north- 
west. "In  less  than  two  hours  the  barometer  again 
began  to  fall  and  the  storm  to  rage  in  heavy  gusts." 
He  bore  again  to  the  southeast,  and  the  weather 
rapidly  improved.  There  can  be  little  doubt  that  but 
for  Captain  Hall's  knowledge  of  the  law  of  cyclones, 
his  ship  and  crew  would  have  been  placed  in  serious 
jeopardy,  since  in  the  heart  of  a  Chinese  typhoon  a 
ship  has  been  known  to  be  thrown  on  her  beams-ends 
when  not  showing  a  yard  of  canvas. 

If  we  consider  the  regions  in  which  cyclones  appear, 
the  paths  they  follow,  and  the  direction  in  which  they 
whirl,  we  shall  be  able  to  form  an  opinion  as  to  their 
origin.  In  the  open  Pacific  Ocean  (as  its  name,  indeed, 
implies)  storms  are  uncommon ;  they  are  infrequent 
also  in  the  South  Atlantic  and  South  Indian  Oceans. 
Around  Cape  Horn  and  the  Cape  of  Good  Hope, 
heavy  storms  prevail,  but  they  are  not  cyclonic,  nor  are 
they  equal  in  fury  and  frequency,  Maury  tells  us,  to 
the  true  tornado.  Along  the  equator,  and  for  several 
degrees  on  either  side  of  it,  cyclones  are  also  unknown. 
If  we  turn  to  a  map  in  which  ocean-currents  are  laid 
down,  we  shall  see  that  in  every  "  cyclone  region  "  there 
is  a  strongly-marked  current,  and  that  each  current 
follows  closely  the  track  which  we  have  denominated 
the  storm- cj.  In  the  North  Atlantic  we  have  the 


182  LIGHT   SCIENCE  FOR  LEISURE  HOURS. 

great  Gulf  Stream,  which  sweeps  from  equatorial 
regions  into  the  Gulf  of  Mexico,  and  thence  across  the 
Atlantic  to  the  shores  of  Western  Europe.  In  the 
South  Indian  Ocean  there  is  the  "south  equatorial 
current"  which  sweeps  past  Mauritius  and  Bourbon, 
and  thence  returns  toward  the  east.  In  the  Chinese 
Sea,  there  is  the  north  equatorial  current,  which 
sweeps  round  the  East-Indian  Archipelago,  and  then 
merges  into  the  Japanese  current.  There  is  also  the 
current  in  the  Bay  of  Bengal,  flowing  through  the 
region  in  which,  as  we  have  seen,  cyclones  are  com- 
monly met  with.  There  are  other  sea-currents  besides 
these  which  yet  breed  no  cyclones.  But  we  may 
notice  two  peculiarities  in  the  currents  we  have  named. 
They  all  flow  from  equatorial  to  temperate  regions, 
and,  secondly,  they  are  all  u  horseshoe  currents."  So 
far  as  we  are  aware,  there  is  but  one  other  current 
which  presents  both  these  pecularities,  namely — the 
great  Australian  current  between  New  Zealand  and 
the  eastern  shores  of  Australia.  "We  have  not  yet 
met  with  any  record  of  cyclones  occurring  over  the 
Australian  current,  but  heavy  storms  are  known  to 
prevail  in  that  region,  and  we  believe  that  when  these 
storms  have  been  studied  as  closely  as  the  storms  in 
better-known  regions,  they  will  be  found  to  present  the 
true  cyclonic  character. 

Now.  if  we  inquire  why  an  ocean-current  travelling 
from  the  equator  should  be  a  "storm-breeder,"  we  shall 


TORNADOES.  183 

find  a  ready  answer.  Such  a  current,  carrying  the 
warmth  of  intertropical  regions  to  the  temperate  zones, 
produces  in  the  first  place,  by  the  mere  difference  of 
temperature,  important  atmospheric  disturbances.  The 
difference  is  so  great,  that  Franklin  suggested  the  use 
of  the  thermometer  in  the  North  Atlantic  Ocean  as  a 
ready  means  of  determining  the  longitude,  since  the 
position  of  the  Gulf  Stream  at  any  given  season  is 
almost  constant. 

Bnt  the  warmth  of  the  stream  itself  is  not  the  only 
cause  of  atmospheric  disturbance.  Over  the  warm 
water  vapor  is  continually  rising ;  and,  as  it  rises,  is 
continually  condensed  (like  the  steam  from  a  loco- 
motive) by  the  colder  air  round.  "An  observer  on 
the  moon,  "  says  Captain  Maury,  "  would,  on  a  winter's 
day,  be  able  to  trace  out  by  the  mist  in  the  air,  the 
path  of  the  Gulf  Stream  through  the  sea. "  But  what 
must  happen  when  vapor  is  condensed?  "We  know 
that  to  turn  water  into  vapor  is  a  process  requiring — 
that  is,  using  up — a  large  amount  of  heat ;  and,  con- 
versely, the  return  of  vapor  to  the  state  of  water  sets 
free  an  equivalent  quantity  of  heat.  The  amount  of 
heat  thus  set  free  from  the  Gulf  Stream  is  thousands 
of  times  greater  than  that  which  would  be  generated 
by  the  whole  coal-supply  annually  raised  in  Great 
Britain.  Here,  then,  we  have  an  efficient  cause  for 
the  wildest  hurricanes.  For  along  the  whole  of  the 
Gulf  Stream,  from  Bernini  to  the  Grand  Banks,  there 


184  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

is  a  channel  of  heated — that  is,  rarefied  air.  Into 
this  channel  the  denser  atmosphere  on  both  sides  is 
continually  pouring,  with  greater  or  less  strength. 
When  a  storm  begins  in  the  Atlantic,  it  always  makes 
for  this  channel,  "  and,  reaching  it,  turns  and  follows 
it  in  its  course,  sometimes  entirely  across  the  Atlantic." 
"  The  southern  points  of  America  and  Africa  have 
won  for  themselves,"  says  Maury,  "  the  name  of  c  the 
stormy  capes,'  but  there  is  not  a  storm-fiend  in  the  wide 
ocean  can  out-top  that  which  rages  along  the  Atlan- 
tic coasts  of  North  America.  The  China  seas  and  the 
North  Pacific  may  vie  in  the  fury  of  their  gales  with 
this  part  of  the  Atlantic,  but  Cape  Horn  and  the  Cape 
of  Good  Hope  cannot  equal  them,  certainly  in  fre- 
quency, nor  do  I  believe,  in  fury."  "We  read  of  a 
West -Indian  storm  so  violent,  that  "it  forced  the 
Gulf  Stream  back  to  its  sources,  and  piled  up  the 
water  to  a  height  of  thirty  feet  in  the  Gulf  of  Mexico. 
The  ship  <  Ledbury  Snow '  attempted  to  ride  out  the 
storm.  When  it  abated,  she  found  herself  high  up  on 
the  dry  land,  and  discovered  that  she  had  let  go  her 
anchor  among  the  tree-tops  on  Elliott's  Key." 

By  a  like  reasoning  we  can  account  for  the  cyclonic 
storms  prevailing  in  the  North  Pacific  Ocean.  Nor 
do  the  tornadoes  which  rage  in  parts  of  the  United 
States  present  any  serious  difficulty.  The  region 
along  which  these  storms  travel  is  the  valley  of  the 
great  Mississippi.  This  river  at  certain  seasons  is  con- 


TORNADOES.  185 

siderably  warmer  than  tlie  surrounding  lands.  From 
its  surface,  also,  aqueous  vapor  is  continually  being 
raised.  When  the  surrounding  air  is  colder,  this 
vapor  is  presently  condensed,  generating  in  the  change 
a  vast  amount  of  heat.  We  have  thus  a  channel  of 
rarefied  air  over  the  Mississippi  Yalley,  and  this  chan- 
nel becomes  a  storm-track,  like  the  corresponding 
channels  over  the  warm  ocean-currents.  The  extreme 
violence  of  land-storms  is  probably  due  to  the  narrow- 
ness of  the  track  within  whicli  they  are  compelled  to 
travel.  For  it  has  been  noticed  that  the  fury  of  a 
sea-cyclone  increases  as  the  range  of  the  "  whirl " 
diminishes,  and  vice  versa. 

There  seems,  however,  no  special  reason  why  cy- 
clones should  follow  the  storm  -c|  in  one  direction 
rather  than  in  the  other.  We  must,  to  understand 
this,  recall  the  fact  that  under  the  torrid  zones  the 
conditions  necessary  for  the  generation  of  storms  prevail 
far  more  intensely  than  in  temperate  regions.  Thus 
the  probability  is  far  greater  that  cyclones  should  be 
generated  at  the  tropical  than  at  the  temperate  end  of 
the  storm  -  ct  Still  it  is  worthy  of  notice,  that  in  the 
land-locked  E"orth  Pacific  Ocean,  true  typhoons  have 
been  known  to  follow  the  storm-track  in  a  direction 
contrary  to  that  commonly  noticed. 

The  direction  in  which  a  true  tornado  whirls  is 
invariably  that  we  have  mentioned.  The  explanation 
of  this  peculiarity  would  occupy  more  space  than  we 


.186  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

can  here  afford.  Those  readers  who  may  wish  to 
understand  the  origin  of  the  law  of  cyclonic  rotation 
should  study  Herschel's  interesting  work  on  Meteor- 
ology. 

The  suddenness  with  which  a  true  tornado  works 
destruction  was  strikingly  exemplified  in  the  wreck  of 
the  steamship  "  San  Francisco."  She  was  assailed  by 
an  extra  tropical  tornado  when  about  300  miles  from 
Sandy  Hook,  on  December  24,  1853.  In  a  few  mo- 
ments she  was  a  complete  wreck !  The  wide  range 
of  a  tornado's  destructiveness  is  shown  by  this,  that 
Colonel  Reid  examined  one  along  whose  track  no  less 
than  110  ships  were  wrecked,  crippled,  or  dismasted. 

(From  Temple  JBar,  December,  1867.) 


VESUVIUS. 

THE  eruption  in  progress,  as  we  write,  from  Mount 
Vesuvius,  and  the  numerous  and  violent  eruptions 
from  this  mountain  during  the  last  two  centuries,  seem 
to  afford  an  answer  to  those  who  think  there  are  traces 
of  a  gradually  diminishing  activity  in  the  earth's  inter- 
nal forces.  That  such  a  diminution  is  taking  place,  we 
may  admit ;  but  that  its  rate  of  progress  is  perceptible 
— that  we  can  point  to  a  time  within  the  historical 
epoch,  nay  even  within  the  limits  of  geological  evi- 
dence, at  which  the  earth's  internal  forces  were  cer- 


VESUVIUS.  187 

tainly  more  active  than  they  are  at  the  present  time — 
may,  we  think,  be  denied  absolutely. 

"When  the  science  of  geology  was  but  young,  and 
its  professors  sought  to  compress  within  a  few  years 
(at  the  outside)  a  series  of  events  which  (we  now 
know)  must  have  occupied  many  centuries,  there  was 
room,  indeed,  for  the  supposition  that  modern  volcanic 
eruptions,  as  compared  with  ancient  outbursts,  are  but 
as  the  efforts  of  children  compared  with  the  work  of 
giants.  And  accordingly,  we  find  a  distinguished 
French  geologist  writing,  even  so  late  as  1829,  that  in 
ancient  times  "  tous  les  phenomenes  geologiques  se 
passaient  dans  des  dimensions  centuples  de  celles 
qu'ils  presentent  aujourd'hui."  But  now  we  have 
such  certain  evidence  of  the  enormous  length  of  the 
intervals  within  which  volcanic  regions  assumed  their 
present  appearance — we  have  such  satisfactory  means 
of  determining  which  of  the  events  occurring  within 
those  intervals  were  or  were  not  contemporary — that 
we  are  safe  from  the  error  of  assuming  that  Nature  at 
a  single  effort  fashioned  widely-extended  districts  just 
as  we  now  see  them.  And  accordingly,  we  have  the 
evidence  of  one  of  the  most  distinguished  of  living 
geologists,  that  there  is  no  volcanic  mass  "  of  ancient 
date,  distinctly  referable  to  a  single  eruption,  which 
can  even  rival  in  volume  the  matter  poured  out  from 
Skaptar  Jokul  in  1783." 

In  the  volcanic  region  of  which  Vesuvius  or  Somma 


188  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

is  the  principal  vent,  we  have  a  remarkable  instance  of 
the  deceptive  nature  of  that  state  of  rest  into  which 
some  of  the  principal  volcanoes  frequently  fall  for 
many  centuries  together.  For  how  many  centuries 
before  the  Christian  era  Vesuvius  had  been  at  rest,  is 
not  known ;  but  this  is  certain,  that,  from  the  landing 
of  the  first  Greek  colony  in  Southern  Italy,  Yesuvius 
gave  no  signs  of  internal  activity.  It  was  recognized 
by  Strabo  as  a  volcanic  mountain,  but  Pliny  did  not 
include  it  in  the  list  of  active  volcanoes.  In  those 
days,  the  mountain  presented  a  very  different  appear- 
ance from  that  which  it  now  exhibits.  In  place  of  the 
two  peaks  now  seen,  there  was  a  single,  somewhat 
flattish,  summit,  on  which  a  slight  depression  marked 
the  place  of  an  ancient  crater.  The  fertile  slopes  of 
the  mountain  were  covered  with  well-cultivated  fields, 
and  the  thriving  cities  Herculaneum,  Pompeii,  and 
Stabiae,  stood  near  the  base  of  the  sleeping  mountain. 
So  little  did  any  thought  of  danger  suggest  itself  in 
those  times,  that  the  bands  of  slaves,  murderers,  and 
pirates  which  flocked  to  the  standard  of  Spartacus 
found  a  refuge,  to  the  number  of  many  thousands, 
within  the  very  crater  itself. 

But  though  Yesuvius  was  at  rest,  the  region  of 
which  Yesuvius  is  the  main  vent  was  far  from  being 
so.  The  island  of  Pithecusa  (the  modern  Ischia)  was 
skaken  by  frequent  and  terrible  convulsions.  It  is 
even  related  that  Prochyta  (the  modern  Procida)  was 


VESUVIUS.  189 

rent  from  Pithecusa  in  the  course  of  a  tremendous 
upheaval,  .though  Pliny  derives  the  name  Prochyta 
(or  "poured  forth")  from  the  supposed  fact  of  this 
island  having  been  poured  forth  by  an  eruption  from 
Ischia.  Far  more  probably,  Prochyta  was  formed 
independently  by  submarine  eruptions,  as  the  volcanic 
islands  near  Santorin  have  been  produced  in  more 
recent  times. 

So  fierce  were  the  eruptions  from  Pithecusa,  that 
several  Greek  colonies  which  attempted  to  settle  on 
this  island  were  compelled  to  leave  it.  About  380 
years  before  the  Christian  era,  colonists  under  King 
Iliero  of  Syracuse,  who  had  built  a  fortress  on 
Pithecusa,  were  driven  away  by  an  eruption.  Nor 
were  eruptions  the  sole  cause  of  danger.  Poisonous 
vapors,  such  as  are  emitted  by  volcanic  craters  after 
eruption,  appear  to  have  exhaled,  at  times,  from  exten- 
sive tracts  on  Pithecusa,  and  thus  to  have  rendered 
the  island  uninhabitable. 

Still  nearer  to  Vesuvius  lay  the  celebrated  Lake 
Avernus.  The  name  Avernus  is  said  to  be  a  corrup- 
tion of  the  Greek  word  Aornos,  signifying  "  without 
birds,"  the  poisonous  exhalations  from  the  waters  of  the 
lake  destroying  all  birds  which  attempted  to  fly  over 
its  surface.  Doubt  has  been  thrown  on  the  destructive 
properties  assigned  by  the  ancients  to  the  vapors 
ascending  from  Avernus.  The  lake  is  now  a  healthy 
and  agreeable  neighborhood,  frequented,  says  Hum- 


190  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

boldt,  by  many  kinds  of  birds,  which  suffer  no  injury 
whatever,  even  when  they  skim  the  very  surface  of  the 
water.  Yet  there  can  be  little  doubt  that  Avernus 
hides  the  outlet  of  an  extinct  volcano  ;  and  long  after 
this  volcano  had  become  inactive,  the  lake  which  con- 
cealed its  site  "  may  have  deserved  the  appellation  of 
6  atri  janua  Ditis,'  emitting,  perhaps,  gases  as  destruc- 
tive of  animal  life  as  those  suffocating  vapors  given 
out  by  Lake  Quilotoa,  in  Quito,  in  1797,  by  which 
whole  herds  of  cattle  were  killed  on  its  shores,  or  as 
those  deleterious  emanations  which  annihilated  all  the 
cattle  in  the  island  of  Lancerote,  one  of  the  Canaries, 
in  1730." 

"While  Ischia  was  in  full  activity,  not  only  was 
Vesuvius  quiescent,  but  even  Etna  seemed  to  be 
gradually  expiring,  so  that  Seneca  ranks  this  volcano 
among  the  number  of  nearly-extinguished  craters.  At 
a  later  epoch,  ^Elian  asserted  that  the  mountain  itself 
was  sinking,  so  that  seamen  lost  sight  of  the  summit  at 
a  less  distance  across  the  seas  than  of  old.  Yet  within 
the  last  two  hundred  years  there  have  been  eruptions 
from  Etna  rivalling,  if  not  surpassing,  in  intensity  the 
convulsions  recorded  by  ancient  historians.  • 

We  shall  not  here  attempt  to  show  that  Vesuvius 
and  Etna  belong  to  the  same  volcanic  sytem,  though 
there  is  reason  not  only  for  supposing  this  to  be  the 
case,  but  for  the  belief  that  all  the  subterranean  regions 
whose  effects  have  been  shown  from  time  to  time  over 


VESUVIUS.  191 

the  district  extending  from  the  Canaries  and  the  Azores, 
across  the  whole  of  the  Mediterranean,  and  into  Syria 
itself,  belong  to  but  one  great  centre  of  internal  action. 
But  it  is  quite  certain  that  Ischia  and  Vesuvius  are 
outlets  from  a  single  source. 

"While  Vesuvius  was  dormant,  resigning  for  a  while 
its  pretensions  to  be  the  principal  vent  of  the  great 
Neapolitan  volcanic  system,  Ischia,  we  have  seen,  was 
rent  by  frequent  convulsions.  But  the  time  was  ap- 
proachiiig  when  Vesuvius  was  to  resume  its  natural 
functions,  and  with  all  the  more  energy  that  they  had 
been  ibr  a  while  suspended. 

In  the  year  63  (after  -Christ)  there  occurred  a 
violent  convulsion  of  the  earth  around  Vesuvius, 
during  which  much  injury  was  done  to  neighboring 
cities,  and  many  lives  were  lost.  From  this  period 
shocks  of  earthquake  were  felt  from  time  to  time  for 
sixteen  years.  These  grew  gradually  more  and  more 
violent,  until  it  began  to  be  evident  that  the  volcanic 
fires  were  about  to  return  to  their  main  vent.  The 
obstruction  which  had  so  long  impeded  the  exit  of  the 
confined  matter  was  not,  however,  readily  removed,  and 
it  was  only  in  August  of  the  year  79,  after  numerous 
and  violent  internal  throes,  that  the  superincumbent 
mass  was  at  length  hurled  forth.  Kocks  and  cinders, 
lava,  sand,  and  scoriae,  were  propelled  from  the  crater, 
and  spread  many  miles  on  every  side  of  Vesuvius. 

We  have   an  interesting    account    of    the    great 


192  LIGHT   SCIENCE  FOR  LEISURE  HOURS. 

eruption  wliicli  followed  in  a  letter  from  the  younger 
Pliny  to  the  younger  Tacitus.  The  latter  had  asked 
for  an  account  of  the  death  of  the  elder  Pliny,  who 
lost  his  life  in  his  eagerness  to  obtain  a  near  view  of 
the  dreadful  phenomenon.  "  He  was  at  that  time," 
says  his  nephew,  "  with  the  fleet  under  his  command 
at  Misenum.  On  August  24th,  about  one  in  the  after- 
noon, my  mother  desired  him  to  observe  a  cloud  of  very 
extraordinary  size  and  shape.  He  had  just  returned 
from  taking  the  benefit  of  the  sun,  and,  after  bathing 
himself  in  cold  water,  and  taking  a  slight  repast,  had 
retired  to  his  study.  He  arose  at  once,  and  went  out 
upon  a  height  whence  he  might  more  distinctly  view 
this  strange  phenomenon.  It  was  not  at  this  distance 
discernible  from  what  mountain  the  cloud  issued,  but 
it  was  found  afterward  that  it  came  from  Yesuvius. 
I  cannot  give  a  more  exact  description  of  its  figure 
than  by  comparing  it  to  that  of  a  pine-tree,  for  it  shot 
up  to  a  great  height  in  the  form  of  a  trunk,  which 
extended  itself  at  the  top  into  a  sort  of  branches ; 
occasioned,  I  suppose,  either  by  a  sudden  gust  of  air 
which  impelled  it,  whose  force  decreased  as  it  advanced 
upward,  or  else  the  cloud  itself,  being  pressed  back 
by  its  own  weight,  expanded  in  this  manner.  The 
cloud  appeared  sometimes  bright,  at  others  dark  and 
spotted,  as  it  was  more  or  less  impregnated  with  earth 
and  cinders." 

These  extraordinary  appearances  attracted  the  cu- 


VESUVIUS.  193 

riosity  of  the  elder  Pliny.  He  ordered  a  small  vessel 
to  be  prepared,  and  started  to  seek  a  nearer  view  of 
the  burning  mountain.  His  nephew  declined  to  ac- 
company him,  being  engaged  with  his  studies.  As 
Pliny  left  the  house,  he  received  a  note  from  a  lady 
whose  house,  being  at  the  foot  of  Vesuvius,  was  in 
imminent  danger  of  destruction.  He  set  out,  accord- 
ingly, with  the  design  of  rendering  her  assistance,  and 
also  of  assisting  others,  "  for  the  villas  stood  extremely 
thick  upon  that  lovely  coast. "  He  ordered  the  galleys 
to  be  put  to  sea,  and  steered  directly  to  the  point  of 
danger,  so  cool  in  the  midst  of  the  turmoil  around  "  as 
to  be  able  to  make  and  dictate  observations  upon  the 
motions  and  figures  of  that  dreadful  scene."  As 
he  approached  Vesuvius,  cinders,  pumice-stones,  and 
black  fragments  of  burning  rock,  fell  on  and  around 
the  ships.  "  They  were  in  danger,  too,  of  running 
aground,  owing  to  the  sudden  retreat  of  the  sea  ;  vast 
fragments,  also,  rolled  down  from  the  mountain  and 
obstructed  all  the  shore."  The  pilot  advising  retreat, 
Pliny  made  the  noble  answer,  "  Fortune  befriends  the 
brave,"  and  bade  him  press  onward  to  Stabise.  Here 
he  found  his  friend  Pomponianus  in  great  consterna- 
tion, already  prepared  for  embarking,  and  waiting  only 
for  a  change  in  the  wind.  Exhorting  Pomponianus  to 
be  of  good  courage,  Pliny  quietly  ordered  baths  to  be 
prepared ;  and  "  having  bathed,  sat  down  to  supper 
with  great  cheerfulness,  or  at  least  (which  is  equally 

9 


194  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

heroic)  with  all  the  appearance  of  it."  Assuring  his 
friends  that  the  flames  which  appeared  in  several 
places  were  merely  burning  villages,  Pliny  presently 
retired  to  rest,  and  "  being  pretty  fat,"  says  his  nephew, 
"and  breathing  hard,  those  who  attended  without 
actually  heard  him  snore."  But  it  became  necessary  to 
awaken  him,  for  the  court  which  led  to  his  room  was 
now  almost  filled  with  stones  and  ashes.  He  got  up 
and  joined  the  rest  of  the  company,  who  were  consult- 
ing on  the  propriety  of  leaving  the  house,  now  shaken 
from  side  to  side  by  frequent  concussions.  They 
decided  on  seeking  the  fields  for  safety  ;  and  fastening 
pillows  on  their  heads,  to  protect  them  from  falling 
stones,  they  advanced  in  the  midst  of  an  obscurity 
greater  than  that  of  the  darkest  night — though  beyond 
the  limits  of  the  great  cloud  it  was  already  broad  day. 
"When  they  reached  the  shore,  they  found  the  waves 
running  too  high  to  suffer  them  safely  to  venture  to 
put  out  to  sea.  Pliny,  "  having  drunk  a  draught  or 
two  of  cold  water,  lay  down  on  a  cloth  that  was  spread 
out  for  him ;  but  at  this  moment  the  flames  and 
sulphurous  vapors  dispersed  the  rest  of  the  company 
and  obliged  him  to  rise.  Assisted  by  two  of  his 
servants,  he  got  upon  his  feet,  but  instantly  fell  down 
dead;  suffocated,  I  suppose,"  says  his  nephew,  "by 
some  gross  and  noxious  vapor,  for  he  always  had 
weak  lungs  and  suffered  from  a  difficulty  of  breathing." 
His  body  was  not  \  found  until  the  third  day  after  his 


VESUVIUS.  195 

death,  when  for  the  first  time  it  was  light  enough  to 
search  for  him.  He  was  found  as  he  had  fallen,  "  and 
looking  more  like  a  man  asleep  than  dead." 

But  even  at  Misenum  there  was  danger,  though 
Yesuvius  is  distant  no  less  than  fourteen  miles. 
The  earth  was  shaken  with  repeated  and  violent 
shocks,  "insomuch,"  says  the  younger  Plrny,  "that 
they  threatened  our  complete  destruction. "  "When 
morning  came,  the  light  was  faint  and  glimmering ; 
the  buildings  around  seemed  tottering  to  their  fall, 
and,  standing  on  the  open  ground,  the  chariots  which 
Pliny  had  ordered  were  so  agitated  backward  and 
forward  that  it  was  impossible  to  keep  them  steady, 
even  by  supporting  them  with  large  stones.  The  sea 
was  rolled  back  upon  itself,  and  many  marine  animals 
were  left  dry  upon  the  shore.  On  the  side  of  Yesuvius, 
a  black  and  ominous  cloud,  bursting  with  sulphurous 
vapors,  darting  out  long  trains  of  fire,  resembling 
flashes  of  lightning,  but  much  larger.  Presently  the 
great  cloud  spread  over  Misenum  and  the  island  of 
Caprese.  Ashes  fell  around  the  fugitives.  On  every 
side  "nothing  was  to  be  heard  but  the  shrieks  of 
women  and  children,  and  the  cries  of  men :  some  were 
calling  for  their  children,  others  for  their  parents, 
others  for  their  husbands,  and  only  distinguishing 
each  other  by  their  voices :  one  was  lamenting  his  own 
fate,  another  that  of  his  family;  some  wished  to  die, 
that  they  might  escape  the  dreadful  fear  of  death; 


196  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

but  the  greater  part  imagined  that  the  last  and  eternal 
night  was  come,  which  was  to  destroy  the  gods  and 
the  world  together. "  At  length  a  light  appeared, 
which  was  not,  however,  the  day,  but  the  forerunner 
of  an  outburst  of  flames.  These  presently  disappeared, 
and  again  the  thick  darkness  spread  over  the  scene. 
Ashes  fell  heavily  upon  the  fugitives,  so  that  they 
were  in  danger  of  being  crushed  and  buried  in  the 
thick  layer  rapidly  covering  the  whole  country.  Many 
hours  passed  before  the  dreadful  darkness  began  slowly 
to  be  dissipated.  "When  at  length  day  returned,  and 
the  sun  was  seen  faintly  shining  through  the  over- 
hanging canopy  of  ashes,  "every  object  seemed 
changed,  being  covered  over  with  white  ashes  as  with 
a  deep  snow." 

It  is  most  remarkable  that  Pliny  makes  no  mention 
in  his  letter  of  the  destruction  of  the  two  populous 
and  important  cities,  Pompeii  and  Herculaneum.  We 
have  seen  that  at  Stabise  a  shower  of  ashes  fell  so 
heavily  that  several  days  before  the  end  of  the  eruption 
the  court  leading  to  the  elder  Pliny's  room  was  begin- 
ning to  be  filled  up ;  and  when  the  eruption  ceased, 
Stabise  was  completely  overwhelmed.  Far  more  sud- 
den, however,  was  the  destruction  of  Pompeii  and 
Herculaneum. 

It  would  seem  that  the  two  cities  were  first  shaken 
violently  by  the  throes  of  the  disturbed  mountain. 
The  signs  of  such  a  catastrophe  have  been  very  com- 


VESUVIUS.  197 

monly  assigned  to  the  earthquake  which  happened  in 
63,  but  it  seems  far  more  likely  that  most  of  them 
belong  to  the  days  immediately  preceding  the  great 
outburst  in  79.  "  In  Pompeii,"  says  Sir  Charles  Lyell, 
"  both  public  and  private  buildings  bear  testimony  to 
the  catastrophe.  The  walls  are  rent,  and  in  many 
places  traversed  by  fissures  still  open."  It  is  probable 
that  the  inhabitants  were  driven  by  these  anticipatory 
throes  to  fly  from  the  doomed  towns.  For  though 
Dion  Cassius  relates  that  "two  entire  cities,  Hercu- 
laneum  and  Pompeii,  were  buried  under  showers  of 
ashes,  while  all  the  people  were  sitting  in  the  theatre," 
yet  "  the  examination  of  the  two  cities  enables  us  to 
prove,"  says  Sir  Charles,  "  that  none  of  the  people  were 
destroyed  in  the  theatre,  and,  indeed,  that  there  were 
very  few  of  the  inhabitants  who  did  not  escape  from 
both  cities.  Yet,"  he  adds,  "  some  lives  were  lost,  and 
there  was  ample. foundation  for  the  tale  in  all  its  most 
essential  particulars." 

We  may  note  here,  in  passing,  that  the  account  of 
the  eruption  given  by  Dion  Cassius,  who  wrote  a 
century  and  a  half  after  the  catastrophe,  is  sufficient 
to  prove  how  terrible  an  impression  had  been  made 
upon  the  inhabitants  of  Campania,  from  whose  descend- 
ants he  in  all  probability  obtained  the  materials  of 
his  narrative.  He  writes  that,  "  during  the  eruption, 
a  multitude  of  men  of  superhuman  stature,  resembling 
giants,  appeared,  sometimes  on  the  mountain,  and 


198  LIGHT   SCIENCE  FOR  LEISURE  HOURS. 

sometimes  in  the  environs;  that  stones  and  smoke 
were  thrown  out,  the  sun  was  hidden,  and  then  the 
giants  seemed  to  rise  again,  while  the  sounds  of  trum- 
pets were  heard  " — with  much  other  matter  of  a  simi- 
lar sort. 

In  the  great  eruption  of  79,  Yesuvius  poured  forth 
lapilli,  sand,  cinders,  and  fragments  of  old  lava,  but  no 
ne^fe.  lava  flowed  from  the  crater.  Nor  does  it  appear 
that  any  lava-stream  was  ejected  during  the  six  erup- 
tions which  took  place  during  the  following  ten  cen- 
turies. In  the  year  1036,  for  the  -first  time,  Yesuvius 
was  observed  to  pour  forth  a  stream  of  molten  lava. 
Thirteen  years  later,  another  eruption  took  place; 
then  90  years  passed  without  disturbance,  and  after 
that  a  long  pause  of  168  years.  During  this  in- 
terval, however,  the  volcanic  system  of  which  Yesu- 
vius is  the  main  but  not  the  only  vent,  had  been 
disturbed  twice.  For  it  is  related  that  in  1198  the 
Solfatara  Lake  crater  was  in  eruption;  and  in  1302, 
Ischia,  dormant  for  at  least  1,400  years,  showed  signs 
of  new  activity.  For  more  than  a  year  earthquakes 
had  convulsed  this  island  from  time  to  time,  and  at 
length  the  disturbed  region  was  relieved  by  the  out- 
burst of  a  lava-stream  from  a  new  vent  on  the  south- 
east of  Ischia.  The  lava-stream  flowed  right  down  to 
the  sea,  a  distance  of  two  miles.  For  two  months, 
this  dreadful  outburst  continued  to  rage ;  many  houses 
were  destroyed ;  and  although  the  inhabitants  of  Ischia 


VESUVI¥S.  199 

were  not  completely  expelled,  as  happened  of  old  with 
the  Greek  colonists,  yet  a  partial  emigration  took 
place. 

The  next  eruption  of  Yesuvius  occurred  in  1306  ; 
and  then  three  centuries  and  a  quarter  passed  during 
which  only  one  eruption,  and  that  an  unimportant  one 
(in  1500),  took  place.  "  It  was  remarked,"  says  Sir 
Charles  Lyell,  "  that  throughout  this  long  interval  of 
rest,  Etna  was  in  a  state  of  unusual  activity,  so  as  to 
lend  countenance  to  the  idea  that  the  great  Sicilian 
volcano  may  sometimes  serve  as  a  channel  of  discharge 
to  elastic  fluids  and  lava  that  would  otherwise  rise  to 
the  vents  in  Campania." 

Nor  was  the  abnormal  activity  of  Etna  the  only 
sign  that  the  quiescence  of  Yesuvius  was  not  to  be 
looked  upon  as  any  evidence  of  declining  energy  in 
the  volcanic  system.  In  1538  a  new  mountain  was 
suddenly  thrown  up  in  the  Phlegrsean  Fields — a  district 
including  within  its  bounds  Pozzuoli,  Lake  Avernus, 
and  the  Solfatara.  The  new  mountain  was  thrown  up 
near  the  shores  of  the  Bay  of  Baiae.  It  is  440  feet 
above  the  level  of  the  bay,  and  its  base  is  about  a  mile 
and  a  half  in  circumference.  The  depth  of  the  crater 
is  421  feet,  so  that  its  bottom  is  only  six  yards  above 
the  level  of  the  bay.  The  spot  on  which  the  mountain 
was  thrown  up  was  formerly  occupied  by  the  Lucrine 
Lake ;  but  the  outburst  filled  up  the  greater  part  of 
the  lake,  leaving  only  a  small  and  shallow  pool. 


200  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

• 

The  accounts  which  have  reached  us  of  the  forma- 
tion of  this  new  mountain  are  not  without  interest. 
Falconi,  who  wrote  in  1538,  mentions  that  several 
earthquakes  took  place  during  the  two  years  preced- 
ing the  outburst,  and  above  twenty  shocks  on  the  day 
and  night  before  the  eruption.  "  The  eruption  began 
on  September  29,  1538.  It  was  on  a  Sunday,  about 
one  o'clock  in  the  night,  when  flames  of  fire  were  seen 
between  the  hot-baths  and  Tripergola.  In  a  short 
time  the  fire  increased  to  such  a  degree  that  it  burst 
open  the  earth  in  this  place,  and  threw  up  a  quantity 
of  ashes  and  pumice-stones,  mixed  with  water,  which 
covered  the  whole  country.  The  next  morning  the 
poor  inhabitants  of  Pozzuoli  quitted  their  habitations 
in  terror,  covered  with  the  muddy  and  black  shower, 
which  continued  the  whole  day  in  that  country — flying 
from  death,  but  with  death  painted  in  their  counte- 
nances. Some  with  their  children  in  their  arms,  some 
with  sacks  full  of  their  goods ;  others  leading  an  ass, 
loaded  with  their  frightened  family,  toward  Naples. 
....  The  sea  had  retired  on  the  side  of  Baiae,  aban- 
doning a  considerable  tract ;  and  the  shore  appeared 
almost  entirely  dry,  from  the  quantity  of  ashes  and 
broken  pumice-stones  thrown  up  by  the  eruption." 

Pietro  Giacomo  di  Toledo  gives  us  some  account 
of  the  phenomena  which  preceded  the  eruption  :  "  That 
plain  which  lies  between  Lake  Avernus,  the  Monte 
Barbaro,  and  the  sea,  was  raised  a  little,  and  many 


VESUVIUS.  201 

cracks  were  made  in  it,  from  some  of  which  water 
issued ;  at  the  same  time  the  sea  immediately  adjoin- 
ing the  plain  dried  up  about  two  hundred  paces,  so 
that  the  fish  were  left  on  the  sand,  a  prey  to  the  inhab- 
itants of  Pozzuoli.  At  last,  on  September  29th,  about 
two  o'clock  in  the  night,  the  earth  opened  near  the 
lake,  and  discovered  a  horrid  mouth,  from  which  were 
furiously  vomited  smoke,  fire,  stones,  and  mud  com- 
posed of  ashes,  making  at  the  time  of  the  opening  a 
noise  like  the  loudest  thunder.  The  stones  which  fol- 
lowed were  by  the  flames  converted  to  pumice,  and 
some  of  these  were  larger  than  an  ox.  The  stones 
went  about  as  high  as  a  cross-bow  will  carry,  and  then 
fell  down,  sometimes  on  the  edge,  and  sometimes  into 
the  mouth  itself.  The  mud  was  of  the  color  of  ashes, 
and  at  first  very  liquid,  then  by  degrees  less  so ;  and 
in  such  quantities  that  in  less  than  twelve  hours,  with 
the  help  of  the  above-mentioned  stones,  a  mountain 
was  raised  of  1,000  paces  in  height.  Not  only  Pozzu- 
oli and  the  neighboring  country  were  full  of  this  mud, 
but  the  city  of  Naples  also ;  so  that  many  of  its  palaces 
were  defaced  by  it.  This  eruption  lasted  two  nights 
and  two  days  without  intermission,  though  not  always 
with  the  same  force ;  the  third  day  the  eruption  ceased, 
and  I  went  up  with  many  people  to  the  top  of  the  new 
hill,  and  saw  down  into  its  mouth,  which  was  a  round 
cavity  about  a  quarter  of  a  mile  in  circumference,  in 
the  middle  of  which  the  stones  which  had  fallen  were 


202  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

boiling  up  just  as  a  caldron  of  water  boils  on  the  fire. 
The  fourth  day  it  began  to  throw  up  again,  and  the 
seventh  day  much  more,  but  still  with,  less  violence 
than  the  first  night.  At  this  time  many  persons  who 
were  on  the  hill  were  knocked  down  by  the  stones  and 
killed,  or  smothered  with  the  smoke." 

And  now,  for  nearly  a  century,  the  whole  district 
continued  in  repose.  Nearly  five  centuries  had  passed 
since  there  had  been  any  violent  eruption  of  Vesuvius 
itself;  and  the  crater  seemed  gradually  assuming  the 
condition  of  an  extinct  volcano.  The  interior  of  the 
crater  is  described  by  Bracini,  who  visited  Vesuvius 
shortly  before  the  eruption  of  1631,  in  terms  that  would 
have  fairly  represented  its  condition  before  the  erup- 
tion of  79  :  "  The  crater  was  five  miles  in  circumfer- 
ence, and  about  a  thousand  paces  deep ;  its  sides  were 
covered  with  brushwood,  and  at  the  bottom  there  was 
a  plain  on  which  cattle  grazed.  In  the  woody  parts, 
wild  boars  frequently  harbored.  In  one  part  of  the 
plain,  covered  with  ashes,  were  three  small  pools,  one 
filled  with  hot  and  bitter  water,  another  salter  than 
the  sea,  and  a  third  hot,  but  tasteless."  But  in  De- 
cember, 1631,  the  mountain  blew  away  the  covering 
of  rock  and  cinders  which  supported  these  woods  and 
pastures.  Seven  streams  of  lava  poured  from  the 
crater,  causing  a  fearful  destruction  of  life  and  prop- 
erty. Resina,  built  over  the  site  of  Ilerculaneum,  was 
entirely  consumed  by  a  raging  lava-stream.  Heavy 


VESUVIUS.  203 

showers  of  rain,  generated  by  the  steam  evolved  dur- 
ing the  eruption,  caused  in  their  turn  an  amount  of 
destruction  scarcely  less  important  than  that  resulting 
from  the  lava-streams.  For,  falling  upon  the  cone, 
and  sweeping  thence  large  masses  of  ashes  and  vol- 
canic dust,  these  showers  produced  destructive  streams 
of  mud,  consistent  enough  to  merit  the  name  of  "  aque- 
ous lava  "  commonly  assigned  to  it. 

An  interval  of  thirty-five  years  passed  before  the 
next  eruption.  But,  since  1666,  there  has  been  a  con- 
tinual series  of  eruptions,  so  that  the  mountain  has 
scarcely  ever  been  at  rest  for  more  than  ten  years 
together.  Occasionally  there  have  been  two  eruptions 
within  a  few  months  ;  and  it  is  well  worthy  of  remark 
that,  during  the  three  centuries  which  have  elapsed 
since  the  formation  of  Monte  ISTuovo,  there  has  been 
no  volcanic  disturbance  in  any  part  of  the  Neapolitan 
volcanic  district  save  in  Yesuvius  alone.  Of  old,  as 
Brieslak  well  remarks,  there  had  been  irregular  dis- 
turbances in  some  part  of  the  Bay  of  Naples  once  in 
every  two  hundred  years ;  the  eruption  of  Solfatara 
in  the  twelfth  century,  that  of  Ischia  in  the  fourteenth, 
and  that  of  Monte  Nuovo  in  the  sixteenth  ;  but  "  the 
eighteenth  has  formed  an  exception  to  the  rule."  It 
seems  clear  that  the  constant  series  of  eruptions  from 
Yesuvius  during  the  past  two  hundred  years  has  suf-r 
ficed  to  relieve  the  volcanic  district  of  which  Yesuvius 
is  the  principal  vent. 


204  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

Of  the  eruptions  wliich  have  disturbed  Vesuvius 
during  the  last  two  centuries,  those  of  1779,  1793-,  and 
1822,  are  in  some  respects  the  most  remarkable. 

Sir  "William  Hamilton  has  given  a  very  interesting 
account  of  the  eruption  of  1779.  Passing  over  those 
points  in  which  this  eruption  resembled  others,  we 
may  note  its  more  remarkable  features.  Sir  William 
Hamilton  says,  that  in  this  eruption  molten  lava  was 
thrown  up  in  magnificent  jets  to  the  height  of  at  least 
10,000  feet.  Masses  of  stones  and  scoriae  were  to  be 
seen  propelled  along  by  these  lava -jets.  Vesuvius 
seemed  to  be  surmounted  by  an  enormous  column  of 
fire.  Some  of  the  jets  were  directed  by  the  wind  tow- 
ard Ottajano ;  others  fell  on  the  cone  of  Vesuvius, 
on  the  outer  circular  mountain  Somma,  and  on  the 
valley  between.  Falling,  still  red  hot  and  liquid,  they 
covered  a  district  more  than  two  miles  and  a  half  wide 
with  a  mass  of  fire.  The  whole  space  above  this 
district,  to  the  height  of  10,000  feet,  was  filled  also 
with  the  falling  and  rising  lava-streams  ;  so  that  there 
was  continually  present  a  body  of  fire  covering  the 
extensive  space  we  have  mentioned,  and  extending 
nearly  two  miles  high.  The  heat  of  this  enormous 
fire-column  was  distinctly  perceptible  at  a  distance  of 
at  least  six  miles  on  every  side. 

The  eruption  of  1793  presented  a  different  aspect. 
Dr.  Clarke  tells  us  that  millions  of  red-hot  stones  were 
propelled  into  the  air  to  at  least  half  the  height  of  the 


VESUVIUS.  205 

cone  itself ;  then  turning,  they  fell  all  around  in  noble 
curves.  They  covered  nearly  half  the  cone  of  Vesuvius 
with  fire.  Huge  masses  of  white  smoke  were  vomited 
forth  by  the  disturbed  mountain,  and  formed  them- 
selves, at  a  height  of  many  thousands  of  feet  above 
the  crater,  into  a  huge,  ever-moving  canopy,  through 
which,  from  time  to  time,  were  hurled  pitch-black  jets 
of  volcanic  dust,  and  dense  vapors,  mixed  with  cas- 
cades of  red-hot  rocks  and  scoriae.  The  rain  which 
fell  from  the  cloud-canopy  was  scalding  hot. 

Dr.  Clarke  was  able  to  compare  the  different  ap- 
pearances presented  by  the  lava  when  it  burst  from 
the  very  mouth  of  the  crater,  and  lower  down  when  it 
had  approached  the  plain.  As  it  rushed  forth  from  its 
imprisonment,  it  streamed  a  liquid,  white,  and  brilliantly 
pure  river,  which  burned  for  itself  a  smooth  channel 
through  a  great  arched  chasm  in  the  side  of  the  moun- 
tain. It  flowed  with  the  clearness  of  "  honey  in  regular 
channels,  cut  finer  than  art  can  imitate,  and  glowing 
with  all  the  splendor  of  the  sun.  Sir  William 
Hamilton  had  conceived,"  adds  Dr.  Clarke,  "  that 
stones  thrown  upon  a  current  of  lava  would  produce 
no  impression.  I  was  soon  convinced  of  the  contrary. 
Light  bodies,  indeed,  of  five,  ten,  and  fifteen  pounds' 
weight,  made  little  or  no  impression,  even  at  the 
source;  but  bodies  of  sixty,  seventy,  and  eighty 
pounds  were  seen  to  form  a  kind  of  bed  on  the  surface 
of  the  lava,  and  floated  away  with  it.  A  stone  of  three 


206  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

hundred- weight,  that  had  been  thrown  out  by  the 
crater,  lay  near  the  source  of  the  current  of  lava.  I 
raised  it  up  on  one  end,  and  then  let  it  fall  in  upon 
the  liquid  lava,  when  it  gradually  sank  beneath  the 
surface  and  disappeared.  If  I  wished  to  describe  the 
manner  in  which  it  acted  upon  the  lava,  I  should  say 
that  it  was  like  a  loaf  of  bread  thrown  into  a  bowl 
of  very  thick  honey,  which  gradually  involves  itself 
in  the  heavy  liquid,  and  then  slowly  sinks  to  the 
bottom." 

But,  as  the  lava  flowed  down  the  mountain-slopes, 
it  lost  its  brilliant  whiteness ;  a  crust  began  to  form 
upon  the  surface  of  the  still  molten  lava,  and  this 
crust  broke  into  innumerable  fragments  of  porous 
matter,  called  scoriae.  Underneath  this  crust — across 
which  Dr.  Clarke  and  his  companions  were  able  to 
pass  without  other  injury  than  the  singeing  of  their 
boots — the  liquid  lava  still  continued  to  force  its  way 
onward  and  downward  past  all  obstacles.  On  its 
arrival  at  the  bottom  of  the  mountain,  says  Dr.  Clarke, 
"  the  whole  current,"  encumbered  with  huge  masses  of 
scoriae,  "  resembled  nothing  so  much  as  a  heap  of 
unconnected  cinders  from  an  iron-foundery,"  "  rolling 
slowly  along,"  he  says  in  another  place,  "  and  falling 
with  a  rattling  noise  over  one  another." 

After  the  eruption  described  by  Dr.  Clarke,  the 
great  crater  gradually  filled  up.  Lava  boiled  up  from 
below,  and  small  craters,  which  formed  themselves 


VESUVIUS.  207 

over  the  bottom  and  sides  of  the  great  one,  poured 
forth  lava  loaded  with  scoriae.  Thus,  up  to  October, 
1822,  there  was  to  be  seen,  in  place  of  a  regular 
crateriform  opening,  a  rough  and  uneven  surface, 
scored  by  huge  fissures,  whence  vapor  was  continually 
being  poured,  so  as  to  form  clouds  above  the  hideous 
heap  of  ruins.  But  the  great  eruption  of  1822  not 
only  flung  forth  all  the  mass  which  had  accumulated 
within  the  crater,  but  wholly  changed  the  appearance 
of  the  cone.  An  immense  abysm  was  formed,  three- 
quarters  of  a  mile  across,  and  extending  2,000  feet 
downward  into  the  very  heart  of  Vesuvius.  Had  the 
lips  of  the  crater  remained  unchanged,  indeed,  the 
depth  of  this  great  gulf  would  have  been  far  greater. 
But  so  terrific  was  the  force  of  the  explosion  that  the 
whole  of  the  upper  part  of  the  cone  was  carried  clean 
away,  and  the  mountain  reduced  in  height  by  nearly  a 
full  fifth  of  its  original  dimensions.  From  the  time  of 
its  formation  the  chasm  gradually  filled  up ;  so  that, 
when  Mr.  Scrope  saw  it  soon  after  the  eruption,  its 
depth  was  reduced  by  more  than  1,000  feet. 

Of  late,  Vesuvius  has  been  as  busy  as  ever.  In 
1833  and  1834  there  were  eruptions;  and  it  is  but 
twelve  years  since  a  great  outburst  took  place.  Then, 
for  three  weeks  together,  lava  streamed  down  the 
mountain-slopes.  A  river  of  molten  lava  swept  away 
the  village  of  Cercolo,  and  ran  nearly  to  the  sea  at 
Ponte  Maddaloni.  There  were  then  formed  ten  small 


208  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

craters  within  the  great  one.  But  these  have  now 
united,  and  pressure  from  beneath  has  formed  a  vast 
cone  where  they  had  been.  The  cone  has  risen  above 
the  rim  of  the  crater,  and  as  we  write  torrents  of  lava 
are  being  poured  forth.  At  first  the  lava  formed  a 
lake  of  fire,  but  the  seething  mass  found  an  outlet,  and 
poured  in  a  wide  stream  toward  Ottajano.  Masses  of 
red-hot  stone  and  rock  are  hurled  forth,  and  a  vast 
canopy  of  white  vapor  hangs  over  Vesuvius,  forming 
at  night,  when  illuminated  by  the  raging  mass  below, 
a  glory  of  resplendent  flame  around  the  summit  of  the 
mountain. 

It  may  seem  strange  that  the  neighborhood  of  so 
dangerous  a  mountain  should  be  inhabited  by  races 
free  to  choose  more  peaceful  districts.  Yet,  though 
Herculaneum,  Pompeii,  and  Stabise,  lie  buried  beneath 
the  lava  and  ashes  thrown  forth  by  Yesuvius,  Portici 
and  Resina,  Torre  del  Greco  and  Torre  dell'  Annun- 
ziata  have  taken  their  place ;  and  a  large  population, 
cheerful  and  prosperous,  flourish  around  the  disturbed 
mountain,  and  over  the  district  of  which  it  is  the  some- 
what untrustworthy  safety-valve. 

It  has,  indeed,  been  well  pointed  out  by  Sir  Charles 
Lyell  that  "the  general  tendency  of  subterranean 
movements,  when  their  effects  are  considered  for  a 
sufficient  lapse  of  ages,  is  eminently  beneficial,  and 
that  they  constitute  an  essential  part  of  that  mechanism 
by  which  the  integrity  of  the  habitable  surface  is  pre- 


EARTHQUAKE  IN   PERU.  209 

served.  "Why  the  working  of  this  same  machinery 
should  be  attended  with  so  much  evil,  is  a  mystery  far 
beyond  the  reach  of  our  philosophy,  and  must  probably 
remain  so  until  we  are  permitted  to  investigate,  not 
our  planet  alone  and  its  inhabitants,  but  other  parts  of 
the  moral  and  material  universe  with  which  they  may 
be  connected.  Could  our  survey  embrace  other  worlds, 
and  the  events,  not  of  a  few  centuries  only,  but  of 
periods  as  indefinite  as  those  with  which  geology  ren- 
ders us  familiar,  some  apparent  contradictions  might 
be  reconciled,  and  some  difficulties  would  doubtless  be 
cleared  up.  But  even  then,  as  our  capacities  are 
finite,  while  the  scheme  of  the  universe  may  be  in- 
finite, both  in  time  and  space,  it  is  presumptuous  to 
suppose  that  all  source  of  doubt  and  perplexity  would 
ever  be  removed.  On  the  contrary,  they  might, 
perhaps,  go  on  augmenting  in  number,  although  our 
confidence  in  the  wisdom  of  the  plan  of  Nature  should 
increase  at  the  same  time;  for  it  has  been  justly  said  " 
(by  Sir  Humphry  Davy)  "  that  the  greater  the  circle 
of  light,  the  greater  the  boundary  of  darkness  by 
which  it  is  surrounded." 

(From  the  Cornhill  Magazine,  March,  1868.) 


THE  EARTHQUAKE  IN  PERU. 

THE  intelligence  published  last  Saturday  is  sufficient 
to  prove  that  the  great  earthquake  which  has  devas- 


210  LIGHT  SCIENCE  FOR  LEISURE   HOURS. 

tated  Peru  fully  equalled,  if  it  did  not  surpass,  the  most 
terrible  catastrophes  which  have  ever  befallen  that 
country.  It  presents,  too,  all  the  features  which  have 
hitherto  characterized  earthquakes  in  this  neighbor- 
hood. These  are  well  worthy  of  careful  study,  and 
appear  to  have  an  important  bearing  on  the  modern 
theory  of  earthquakes. 

It  has  been  commonly  held  that  the  seat  of  disturb- 
ance in  the  earthquakes  which  have  shaken  the  country 
west  of  the  Andes  has  lain  always  at  some  point  or 
other  beneath  that  range  of  mountains.  The  fact  that 
several  large  volcanoes  are  found  in  the  Cordilleras 
has  seemed  confirmatory  of  this  view.  The  accounts 
we  have  also  of  the  great  earthquake  at  Riobamba  in 
1797,  seem  only  explicable  by  supposing  that  the  seat 
of  disturbance  lay  almost  immediately  beneath  that 
city.  The  inhabitants  were  flung  vertically  upward 
into  the  air,  and  to  such  a  height  that  Humboldt  found 
the  skeletons  of  many  of  them  on  the  summit  of  the 
hill  La  Culca,  on  the  farther  side  of  the  small  river  on 
which  Kiobamba  is  built.  The  ruins  of  many  houses 
were  also  flung  to  the  same  spot.  Here,  therefore, 
was  evidence  of  that  vertical  (or,  as  Humboldt  ex- 
presses it,  explosive)  force  which  is  only  to  be  looked 
for  immediately  above  the  centre  of  concussion. 

Yet  the  consideration  of  the  evidence  afforded  by 
the  news  we  have  just  published,  seems  at  first  sight 
somewhat  opposed  to  this  view,  and  to  point  rather  to 


EARTHQUAKE  IN  PERU.  211 

a  seat  of  disturbance  lying  considerably  to  the  west  of 
the  Peruvian  shores.  "  At  Chala,"  says  our  informant, 
"  the  sea  receded,  and  a  wave  rose  fifty  feet,  and  re- 
turned, spreading  into  the  town  a  distance  of  about  a 
thousand  feet.  Three  successive  times  every  thing 
within  range  was  swept  away,  followed  by  twelve 
shocks  of  earthquake,  lasting  from  three  seconds  to 
two  minutes."  The  arrival  of  great  sea-waves  before 
the  land-shocks  were  felt  seems  decisively  to  indicate 
that  the  seat  of  disturbance  lay  beneath  the  ocean  and 
not  beneath  the  land.  "We  are  disposed  to  believe, 
however,  that  in  the  confusion  of  mind  naturally  re- 
sulting from  the  occurrence  of  so  terrible  a  catastrophe, 
the  sequence  of  events  may  not  have  been  very  closely 
attended  to,  for  in  other  places  the  arrival  of  the  great 
sea-wave  is  distinctly  described  as  following  the  occur- 
rence of  the  earth-shock.  At  Arica,  for  example,  a 
considerable  interval  would  seem  to  have  elapsed  before 
the  terrible  sea-wave,  which  has  always  characterized 
Peruvian  earthquakes,  poured  in  upon  the  town.  The 
agent  of  the  Pacific  Steam  Navigation  Company,  whose 
house  had  been  destroyed  by  the  earth-shock,  saw  the 
great  sea-wave  while  he  was  flying  toward  the  hills. 
He  writes  :  "  While  passing  toward  the  hills,  with  the 
earth  shaking,  a  great  cry  went  up  to  heaven.  The 
sea  had  retired.  On  clearing  the  town,  I  looked  back 
and  saw  that  the  vessels  were  being  carried  irresistibly 
seaward.  In  a  few  minul.es  the  sea  stopped,  and  then 


212  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

arose  a  mighty  wave  fifty  feet  high,  and  came  in  with 
a  fearful  rush,  carrying  every  thing  before  it  in  terrible 
majesty.  The  whole  of  the  shipping  came  back,  speed- 
ing toward  inevitable  doom.  In  a  few  minutes  all  was 
completed — every  vessel  was  either  on  shore  or  bottom 
upward."  This,  then,  was  undoubtedly  the  great  sea- 
wave,  as  compared  with  the  minor  waves  of  disturbance 
which  characterize  all  earthquakes  near  the  shores  of 
the  ocean. 

One  remarkable  feature  in  this  terrible  earthquake 
is  the  enormous  range  of  country  affected  by  it.  From 
Quito  southward  as  far  as  Iquique — or,  in  other  words, 
for  a  distance  considerably  exceeding  a  full  third  part 
of  the  whole  length  of  the  South  American  Andes — 
the. shock  was  felt  with  the  most  terrible  distinctness. 
"We  have  yet  to  learn  how  much  farther  to  the  north 
and  south,  and  how  far  inland  on  the  eastern  slopes  of 
the  Andes,  the  shock  was  experienced.  But  there  can 
be  little  doubt  that  the  disturbed  country  was  equal  to 
at  least  a  fourth  of  Europe. 

The  portion  of  the  Andes  thus  disturbed  seems  to 
be  distinct  from  the  part  to  which  the  great  Chilian 
earthquakes  belong.  The  difference  in  character  be- 
tween the  Peruvian  and  Chilian  earthquakes  is  a  sin- 
gular and  interesting  phenomenon.  The  difference 
corresponds  to  a  feature  long  since  pointed  out  by  Sir 
Charles  Lyell — the  alternation,  011  a  grand  scale,  of 
districts  of  active  with  those  of  extinct  volcanoes.  It 


EARTHQUAKE   IN   PERU.  213 

is  said  that  in  Chili  a  year  scarcely  ever  passes  without 
shocks  of  earthquake  being  felt ;  in  certain  regions,  not 
even  a  month.  A  similar  persistence  of  earthquake 
disturbance  characterizes  Peru.  Yet,  although  both 
districts  are  shaken  in  this  manner,  there  seems  to  be 
a  distinct  evidence  of  alternating  disturbance  as  re- 
spects the  occurrence  of  great  earthquakes.  Thus,  in 
1797,  took  place  the  terrible  earthquake  of  Riobamba. 
Then,  thirty  years  later,  a  series  of  great  earthquakes 
shook  Chili,  permanently  elevating  the  whole  line  of 
coast  to  the  height  of  several  feet.  Now,  again,  after 
another  interval  of  about  thirty  years,  the  Andes  are 
disturbed  by  a  great  earthquake,  and  this  time  it  is  the 
Peruvian  Andes  which  experience  the  shock.  Between 
Chili  and  Peru  there  is  a  space  upward  of  five  hundred 
miles  long,  in  which  no  volcanic  action  has  been  ob- 
served. Singularly  enough,  this  very  portion  of  the 
Andes,  to  which  one  would  imagine  the  Peruvians  and 
Chilians  would  fly  as  to  a  region  of  safety,  is  the  part 
most  thinly  inhabited,  insomuch  that,  as  Yon  Buch 
observes,  it  is  in  some  places  entirely  deserted. 

Near  Quito  the  trembling  of  the  earth  is  almost  in- 
cessant, according  to  M.  Boussingault.  He  considers 
that  the  frequency  of  the  movement  is  due  rather  to 
the  continual  falling  in  of  masses  of  rock  which  have 
been  fractured  in  recent  earthquakes,  than  to  the  per- 
sistence of  subterranean  action.  He  adds  that  the 
height  of  several  mountains  in  the  Andes  has  diminished 


£14  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

in  modern  times.  He  refers,  doubtless,  to  the  Peruvian 
and  Colombian  Andes,  and  not  to  the  Chilian.  In  the 
latter  portion  of  the  range  there  must  be  a  continual 
increase  of  height,  since  each  earthquake  in  Chili  has 
produced  a  perceptible  recession  of  the  sea.  Darwin, 
indeed,  relates  that  near  Valparaiso  he  saw  beds  of 
sea-shells  belonging  to  recent  species  at  a  height  of 
about  a  quarter  of  a  mile  abovo  the  present  sea-level ; 
and  he  concluded  that  the  land  had  been  raised  to  this 
height  by  a  series  of  such  small  elevations  as  were  ob- 
served to  have 'taken  place  during  the  earthquakes  of 
1822,  1835,  and  1837.  That  a  contrary  process  should 
be  going  on  in  Peru,  confirms  the  idea  that  a  sort  of 
undulatory  or  balancing  motion  is  taking  place — one 
long  stretch  of  the  Cordilleras  rising  while  another  is 
sinking.  A  tradition  prevails  among  the  Indians  of 
Lican  that  the  mountain  called  L' Altar,  or  Cassac 
Urcu — which  means  "  the  chief" — was  once  the  highest 
of  the  sub-equatorial  Andes,  being  higher  even  than 
Chimborazo ;  but,  adds  the  tradition,  in  the  reign  of 
Quainia  Abomatha,  before  the  discovery  of  America,  a 
prodigious  eruption  took  place  which  lasted  no  less 
than  eight  years,  and  brought  down  the  summit  of  the 
mountain.  M.  Boussingault  states  that  the  fragments 
of  trachyte  which  once  formed  the  summit  of  this  cele- 
brated mountain  are  now  spread  over  the  plain.  At 
present  Cotopaxi  is  the  loftiest  volcano  of  the  Cordil- 
leras, its  height  being  no  less  than  18,858  feet.  'No 


EARTHQUAKE   IN  PERU.  215 

mountain  lias  ever  been  the  seat  of  such  terrible  and 
destructive  eruptions  as  those  which  have  burst  forth 
from  Cotopaxi.  The  intensity  of  the  heat  which  pre- 
vails during  eruption  will  be  readily  gathered  from  the 
circumstance  that  in  January,  1803,  the  enormous  bed 
of  snow  which  usually  covers  the  cone  of  the  volcano 
was  dissolved  in  a  single  night. 

It  would  seem  that  the  Mexican  volcanoes  also 
belong  to  the  same  region  of  disturbances.  Near  the 
Isthmus  of  Panama  the  great  Cordillera  of  the  Andes 
lowers  itself  to  the  height  of  about  800  feet,  and  beyond 
begins  the  continuation  of  the  volcanic  chain  in  Cen- 
tral America  and  Mexico.  JSTor  are  the  volcanoes  of 
the  West  Indian  or  Caribbee  Islands  wholly  discon- 
nected with  the  region  of  disturbance  in  Southern 
America.  And  it  is  rather  singular  that  even  the 
earthquakes  which  have  occurred  in  the  valley  of  the 
Mississippi  seem  to  be  connected  with  the  West  Indian 
and  South  American  volcanic  region.  The  violent 
earthquakes  which  took  place  at  New  Madrid  in  1812, 
occurred  at  exactly  the  same  time  as  the  earthquake  of 
Paranas,  "  so  that  it  is  possible,"  says  Sir  Charles  Lyell, 
"  that  these  two  points  are  part  of  one  volcanic  region." 

(From  the  Daily  News,  September  18,  1868.) 


216  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 


THE   GREATEST  SEA-WAVE  EVER  KNOWN. 

ON  August  13,  1868,  one  of  the  most  terrible  ca- 
lamities which  has  ever  visited  a  people  befell  the  un- 
fortunate inhabitants  of  Peru.  In  that  land  earth- 
quakes are  nearly  as  common  as  rain-storms  are  with 
us  ;  and  shocks  by  which  whole  cities  are  changed  into 
a  heap  of  ruins  are  by  no  means  infrequent.  Yet  even 
in  Peru,  "  the  land  of  earthquakes,"  as  liumboldt  has 
termed  it,  no  such  catastrophe  as  that  of  August,  1868, 
had  occurred  within  the  memory  of  man.  It  was  not 
one  city  which  was  laid  in  ruins,  but  a  whole  empire. 
Those  who  perished  were  counted  by  tens  of  thousands, 
while  the  property  destroyed  by  the  earthquake  was 
valued  at  millions  of  pounds  sterling. 

Although  so  many  months  have  passed  since  this 
terrible  calamity  took  place,  scientific  men  have  been 
busily  engaged  until  quite  recently  in  endeavoring  to 
ascertain  the  real  significance  of  the  various  events 
which  were  observed  during  and  after  the  occurrence 
of  the  earthquake.  The  geographers  of  Germany  have 
taken  a  special  interest  in  interpreting  the  evidence 
afforded  by  this  great  manifestation  of  Nature's  powers. 
Two  papers  have  been  written  recently  on  the  great 
earthquake  of  August  13,  1868,  one  by  Professor  von 
Hochstetter,  the  other  by  Herr  von  Tsclmdi,  which 
present  an  interesting  account  of  the  various  effects. 


A  GREAT   SEA- WAVE.  217 

by  land  and  by  sea,  which  resulted  from  the  tremen- 
dous upheaving  force  to  which  the  western  flanks  of 
the  Peruvian  Andes  were  subjected  on  that  day.  The 
effects  on  land,  although  surprising  and  terrible,  yet 
only  differ  in  degree  from  those  which  have  been  ob- 
served in  other  earthquakes.  But  the  progress  of  the 
great  sea-wave  which  was  generated  by  the  upheaval 
of  the  Peruvian  shores  and  propagated  over  the  whole 
of  the  Pacific  Ocean  differs  altogether  from  any  earth- 
quake phenomena  before  observed.  Other  earthquakes 
have  indeed  been  followed  by  oceanic  disturbances ; 
but  these  have  been  accompanied  by  terrestrial  mo- 
tions, so  as  to  suggest  the  idea  that  they  had  been 
caused  by  the  motion  of  the  sea-bottom,  or  of  the  neigh- 
boring land.  In  no  instance  has  it  ever  before  been 
known  that  a  well-marked  wave  of  enormous  propor- 
tions should  have  been  propagated  over  the  largest 
ocean-tract  on  our  globe,  by  an  earth-shock  whose 
direct  action  was  limited  to  a  relatively  small  region, 
and  that  region  not  situated  in  the  centre,  but  on  one 
side  of  the  wide  area  traversed  by  the  wave. 

"We  propose  to  give  a  brief  sketch  of  the  history  of 
this  enormous  sea-wave.  In  the  first  place,  however, 
it  may  be  well  to  remind  the  reader  of  a  few  of  the 
more  prominent  features  of  the  great  shock  to  which 
this  wave  owed  its  origin. 

It  was  at  Arequipa,  at  the  foot  of  the  lofty  volcanic 
mountain  Misti,  that  the  most  terrible  effects  of  the 

10 


218  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

great  earthquake  were  experienced.     Within  historic 
times  Misti  has  poured  forth  no  lava-streams,  but  that 
the  volcano  is  not  extinct  is  clearly  evidenced  by  the 
fact  that  in  1542  an  enormous  mass  of  dust  and  ashes 
was  vomited  forth  from  its  crater.     On  August  13, 
1868,  Misti  showed  no  signs  of  being  disturbed.     So 
far  as  their  volcanic  neighbor  was  concerned,  the  44,000 
inhabitants  of  Arequipa  had  no  reason  to  anticipate 
the  catastrophe  which  presently  befell  them.     At  live 
minutes  past  five  an  earthquake-shock  was  experienced, 
which,  though  severe,  seems  to  have  worked  little  mis- 
chief.    Half  a  minute  later,  however,  a  terrible  noise 
was  heard  beneath  the  earth ;   a  second  shock  more 
violent  than  the  first  was  felt ;  and  then  began  a  sway- 
ing motion,  gradually  increasing  in  intensity.     In  the 
course  of  the  first  minute  this  motion  had  become  so 
violent  that  the  inhabitants  ran  in  terror  out  of  their 
houses  into  the  streets  and  squares.     In  the  next  two 
minutes  the  swaying  movement  had  so  increased  that 
the  more  lightly-built  houses  were  cast  to  the  ground, 
and  the  flying  people  could  scarcely  keep  their  feet. 
"  And  now,"  says  Yon  Tschudi,  "  there  followed  during' 
two  or  three  minutes  a  terrible  scene.     The  swaying 
motion  which  had  hitherto  prevailed   changed  into 
fierce  vertical  upheaval.     The  subterranean  roaring 
increased  in  the  most  terrifying  manner :   then  were 
heard  the  heart-piercing  shrieks  of  the  wretched  people, 
the  bursting  of  walls,  the  crashing  fall  of  houses  and 


A  GREAT  SEA-WAVE.  219 

churches,  while  over  all  rolled  thick  clouds  of  a  yel- 
lowish-black dust,  which,  had  they  been  poured  forth 
many  minutes  longer,  would  have  suffocated  thousands." 
Although  the  shocks  had  lasted  but  a  few  minutes,  the 
whole  town  was  destroyed.  Not  one  building  remained 
uninjured,  and  there  were  few  which  did  not  lie  in 
shapeless  heaps  of  ruins. 

At  Tacna  and  Arica,  the  earth-shock  was  less 
severe,  but  strange  and  terrible  phenomena  followed 
it.  At  the  former  place  a  circumstance  occurred,  the 
cause  and  nature  of  which  yet  remain  a  mystery. 
About  three  hours  after  the  earthquake — in  other 
words,  at  about  eight  o'clock  in  the  evening — an  in- 
tensely brilliant  light  made  its  appearance  above  the 
neighboring  mountains.  It  lasted  for  fully  half  an 
hour,  and  has  been  ascribed  to  the  eruption  of  some  as 
yet  unknown  volcano. 

At  Arica  the  sea-wave  produced  even  more  de- 
structive effects  than  had  been  caused  by  the  earth- 
quake. About  twenty  minutes  after  the  first  earth- 
shock,  the  sea  was  seen  to  retire,  as  if  about  to  leave 
the  shores  wholly  dry;  but  presently  its  waters  re- 
turned with  tremendous  force.  A  mighty  wave, 
whose  length  seemed  immeasurable,  was  seen  advancing 
like  a  dark  wall  upon  the  unfortunate  town,  a  large 
part  of  which  was  overwhelmed  by  it.  Two  ships,  the 
Peruvian  corvette  "  America  "  and  the  United  States 
"  double-ender  "  "  Wateree,"  were  carried  nearly  half 


220  LIGHT  SCIENCE  FOR  LEISURE   HOURS. 

a  mile  to  the  north  of  Arica,  beyond  the  railroad 
which  runs  to  Tacna,  and  there  left  stranded  high  and 
dry.  This  enormous  wave  was  considered  by  the  Eng- 
lish vice-consul  at  Arica  to  have  been  fully  fifty  feet  in 
height. 

At  Chala,  three  such  waves  swept  in  after  the  first 
shocks  of  earthquake.  -  They  overflowed  nearly  the 
whole  of  the  town,  the  sea  passing  more  than  half  a 
mile  beyond  its  usual  limits. 

At  Islay  and  Iquique  similar  phenomena  were  mani- 
fested. At  the  former  town  the  sea  flowed  in  no  less 
than  five  times,  and  each  time  with  greater  force. 
Afterward  the  motion  gradually  diminished,  but  even 
an  hour  and  a  half  after  the  commencement  of  this 
strange  disturbance,  the  waves  still  ran  forty  feet 
above  the  ordinary  level.  At  Iquique,  the  people 
beheld  the  inrushing  wave  while  it  was  still  a  great 
way  off.  A  dark-blue  mass  of  water,  some  fifty  feet 
in  height,  was  seen  sweeping  in  upon  the  town  with 
inconceivable  rapidity.  An  island  lying  before  the 
harbor  was  completely  submerged  by  the  great  wave, 
which  still  came  rushing  on,  black  with  the  mud  and 
slime  it  had  swept  from  the  sea-bottom.'  Those  who 
witnessed  its  progress  from  the  upper  balconies  of  their 
houses,  and  presently  saw  its  black  mass  rushing  close 
beneath  their  feet,  looked  on  their  safety  as  a  miracle. 
Many  buildings  were  indeed  washed  away,  and  in  the 
low-lying  parts  of  the  town  there  was  a  terrible  loss  of 


A  GREAT  SEA-WAVE.  221 

MQ.  After  passing  far  inland,  the  wave  slowly  re- 
turned seaward,  and  strangely  enough,  the  sea,  which 
elsewhere  heaved  and  tossed  for  hours  after  the  first 
great  wave  had  swept  over  it,  here  came  soon  to  rest. 

At  Callao  a  yet  more  singular  instance  was  afford- 
ed of  the  effect  which  circumstances  may  have  upon 
the  motion  of  the  sea  after  a  great  earthquake  has  dis- 
turbed it.  In  former  earthquakes  Callao  has  suffered 
terribly  from  the  effects  of  the  great  sea-wave.  In 
fact,  on  two  occasions  the  whole  town  has  been  de- 
stroyed, and  nearly  all  its  inhabitants  have  been 
drowned,  through  the  inrush  of  precisely  such  waves 
as  flowed  into  the  ports  of  Arica  and  Chala.  But  upon 
this  occasion  the  centre  of  subterranean  disturbance 
must  have  been  so  situated  that  either  the  wave  was 
diverted  from  Callao,  or  more  probably  two  waves 
reached  Callao  from  different  sources  and  at  different 
times,  so  that  the  two  undulations  partly  counteracted 
each  other.  Certain  it  is  that,  although  the  water 
retreated  strangely  from  the  coast  near  Callao,  inso- 
much that  a  wide  tract  of  the  sea-bottom  was  un- 
covered, there  was  no  inrushing  wave  comparable  with 
those  described  above.  The  sea  afterward  rose  and 
fell  in  an  irregular  manner,  a  circumstance  confirming 
the  supposition  that  the  disturbance  was  caused  by  two 
distinct  oscillations.  Six  hours  after  the  occurrence  of 
the  earth-shock,  the  double  oscillations  seemed  for  a 
while  to  have  worked  themselves  into  unison,  for  at 


222  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

this  time  three  considerable  waves  rolled  in  upon  the 
town.  But  clearly  these  waves  must  not  be  compared 
with  those  which  in  other  instances  had  made  their 
appearance  within  half  an  hour  of  the  earth-throes. 
There  is  little  reason  to  doubt  that  if  the  separate 
oscillations  had  reenforced  each  other  earlier,  Callao 
would  have  been  completely  destroyed.  As  it  was,  a 
considerable  amount  of  mischief  was  effected ;  but  the 
motion  of  the  sea  presently. became  irregular  again,  and 
so  continued  until  the  morning  of  August  14th,  when 
it  began  to  ebb  with  some  regularity.  But  during  the 
14th  there  were  occasional  renewals  of  the  irregular 
motion,  and  several  days  elapsed  before  the  regular 
ebb  and  flow  of  the  sea  were  resumed. 

Such  were  among  the  phenomena  presented  in  the 
region  where  the  earthquake  itself  was  felt.  It  will 
be  seen  at  once  that  within  this  region,  or  rather 
along  that  portion  of  the  sea-coast  which  falls  within 
the  central  region  of  disturbance,  the  true  character  of 
the  sea-wave  generated  by  the  earthquake  could  not 
be  recognized.  If  a  rock  fall  from  a  lofty  cliff  into  a 
comparatively  shallow  sea,  the  water  around  the  place 
where  the  rock  has  fallen  is  disturbed  in  an  irregular 
manner.  The  sea  seems  at  one  place  to  leap  up  and 
down ;  elsewhere  one  wave  seems  to  beat  against 
another,  and  the  sharpest  eye  can  detect  no  law  in  the 
motion  of  the  seething  waters.  But  presently,  outside 
the  scene  of  disturbance,  a  circular  wave  is  seen  to 


A  GREAT  SEA-WAVE.  223 

form,  and  if  the  motion  of  this  wave  be  watched,  it  is 
seen  to  present  the  most  striking  contrast  with  the 
turmoil  and  confusion  at  its  centre.  It  sweeps  onward 
and  outward  in  a  regular  undulation.  Gradually  it 
loses  its  circular  figure  (unless  the  sea-bottom  happens 
to  be  unusually  level),  showing  that  although  its 
motion  is  everywhere  regular,  it  is  not  everywhere 
equally  swift.  A  wave  of  this  sort,  though  incom- 
parably vaster,  swept  swiftly  away  on  every  side  from 
the  scene  of  the  great  earthquake  near  the  Peruvian 
Andes.  It  has  been  calculated  that  the  width  of 
this  wave  varied  from  one  million  to  five  million  feet, 
or  roughly  from  200  to  1,000  miles,  while,  when  in 
mid-Pacific,  the  length  of  the  wave,  measured  along 
its  summit  in  a  widely-curved  path  from  one  side  to 
another  of  the  great  ocean,  cannot  have  been  less  than 
8,000  miles. 

We  cannot  tell  how  deep-seated  was  the  centre  of 
subterranean  action ;  but  there  can  be  no  doubt  it  was 
very  deep  indeed,  because  otherwise  the  shock  felt  in 
towns  separated  from  each  other  by  hundreds  of  miles 
could  not  have  been  so  nearly  contemporaneous. 
Therefore  the  portion  of  the  earth's  crust  upheaved 
must  have  been  enormous,  for  the  length  of  the 
region  where  the  direct  effects  of  the  earthquake  were 
perceived  is  estimated  by  Professor  von  Hochstetter 
at  no  less  than  240  miles.  The  breadth  of  the  region 
is  unknown,  because  the  slope  of  the  Andes  on  one 


224  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

side  and  the  ocean  on  the  other  concealed  the  motion 
of  the  earth's  crust. 

The  great  ocean-wave  swept,  as  we  have  said,  in  all 
directions  around  the  scene  of  the  earth-throe.  Over 
a  large  part  of  its  course  its  passage  was  unnoted, 
because  in  the  open  sea  the  effects  even  of  so  vast  an 
undulation  could  not  be  perceived.  A  ship  would 
slowly  rise  as  the  crest  of  the  great  wave  passed  under 
her,  and  then  as  slowly  sink  again.  This  may  seem 
strange,  at  first  sight,  when  it  is  remembered  that  in 
reality  the  great  sea-wave  we  are  considering  swept  at 
the  rate  of  three  or  four  hundred  sea-miles  an  hour 
over  the  larger  part  of  the  Pacific.  But  when  the 
true  character  of  ocean-waves  is  understood,  when  it  is 
remembered  that  there  is  no  transference  of  the  water 
itself  at  this  enormous  rate,  but  simply  a  transmission 
of  motion  (precisely  as  when  in  a  high  wind  waves 
sweep  rapidly  over  a  cornfield,  while  yet  each  corn- 
stalk remains  fixed  in  the  ground),  it  will  be  seen 
that  the  effects  of  the  great  sea-wave  could  only  be 
perceived  near  the  shore.  Even  there,  as  we  shall 
presently  see,  there  was  much  to  convey  the  impres- 
sion that  the  land  itself  was  rising  and  falling  rather 
than  that  the  deep  was  moved.  But  among  the 
hundreds  of  ships,  which  were  sailing  upon  the  Pacific 
when  its  length  and  breadth  were  traversed  by  the 
great  sea-wave,  there  was  not  one  in  which  any  un- 
usual motion  was  perceived. 


A  GREAT   SEA-WAVE.  225 

In  somewhat  less  than  three  hours  after  the  occur- 
rence of  the  earthquake,  the  ocean-wave  inundated  the 
port  of  Coquimbo,  on  the  Chilian  seaboard,  some  800 
miles  from  Arica.  An  hour  or  so  later  it  had  reached 
Constitucion,  450  miles  farther  south;  and  here  for 
some  three  hours  the  sea  rose  and  fell  with  strange 
violence.  Farther  south,  along  the  shore  of  Chili, 
even  to  the  island  of  Chiloe,  the  shore-wave  travelled, 
though  with  continually  diminishing  force,  owing, 
doubtless,  to  the  resistance  which  the  irregularities  of 
the  shore  opposed  to  its  progress. 

The  northerly  shore-wave  seems  to  have  been  more 
considerable ;  and  a  moment's  study  of  a  chart  of  the 
two  Americas  will  show  that  this  circumstance  is 
highly  significant.  "When  we  remember  that  the 
principal  effects  of  the  land-shock  were  experienced 
within  that  angle  which  the  Peruvian  Andes  form 
with  the  long  north -and-south  line  of  the  Chilian  and 
Bolivian  Andes,  we  see  at  once  that  had  the  centre  of 
the  subterranean  action  been  near  the  scene  where  the 
most  destructive  effects  were  perceived,  no  sea-wave, 
or  but  a  small  one,  could  have  been  sent  toward  the 
shores  of  North  America.  The  projecting  shores  of 
northern  Peru  and  Ecuador  could  not  have  failed  to 
divert  the  sea-wave  toward  the  west ;  and  though  a 
reflected  wave  might  have  reached  California,  it  would 
only  have  been  after  a  considerable  interval  of  time, 
and  with  dimensions  much  less  than  those  of  the  sea- 


226  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

wave  which  travelled  southward.  When  we  see  that, 
on  the  contrary,  a  wave  of  even  greater  proportions 
travelled  toward  the  shores  of  North  America,  we 
seem  forced  to  the  conclusion  that  the  centre  of  the 
subterranean  action  must  have  been  so  far  to  the  west 
that  the  sea-wave  generated  by  it  had  a  free  course  to 
the  shores  of  California. 

Be  this  as  it  may,  there  can  be  no  doubt  that  the 
wave  which  swept  the  shores  of  Southern  California, 
rising  upward  of  sixty  feet  above  the  ordinary  sea- 
level,  was  absolutely  the  most  imposing  of  all  the 
indirect  effects  of  the  great  earthquake.  "When  we 
consider  that  even  in  San  Pedro  Bay,  fully  five  thou- 
sand miles  from  the  centre  of  disturbance,  a  wave 
twice  the  height  of  an  ordinary  house  rolled  in  with 
unspeakable  violence  only  a  few  hours  after  the  occur- 
rence of  the  earth-throe,  we  are  most  strikingly  im- 
pressed with  the  tremendous  energy  of  the  earth's 
movement. 

Turning  to  the  open  ocean,  let  us  track  the  great 
wave  on  its  course  past  the  multitudinous  islands  which 
dot  the  surface  of  the  great  Pacific. 

The  inhabitants  of  the  Sandwich  Islands,  which  lie 
about  6,300  miles  from  Arica,  might  have  imagined 
themselves  safe  from  any  effects  which  could  be  pro- 
duced by  an  earthquake  taking  place  so  far  away  from 
them.  But  on  the  night  between  August  13th  and  14th, 
the  sea  around  this  island-group  rose  in  a  surprising 


A  GREAT  SEA-WAVE.  227 

manner,  insomuch  that  many  thought  the  islands  were 
sinking,  and  would  shortly  subside  altogether  beneath 
the  waves.  Some  of  the  smaller  islands,  indeed,  were 
for  a  time  completely  submerged.  Before  long,  how- 
ever, the  sea  fell  again,  and  as  it  did  so  the  observers 
"  found  it  impossible  to  resist  the  impression  that  the 
islands  were  rising  bodily  out  of  the  water."  For  no 
less  than  three  days  this  strange  oscillation  of  the  sea 
continued  to  be  experienced,  the  most  remarkable  ebbs 
and  floods  being  noticed  at  Honolulu,  on  the  island  of 
Woahoo. 

But  the  sea-wave  swept  onward  far  beyond  these 
islands. 

At  Yokohama,  in  Japan,  more  than  10,500  miles 
from  Arica,  an  enormous  wave  poured  in  on  August 
14th,  but  at  what  hour  we  have  no  satisfactory  record. 
So  far  as  distance  is  concerned,  this  wave  affords  most 
surprising  evidence  of  the  stupendous  nature  of  the 
disturbance  to  which  the  waters  of  the  Pacific  Ocean 
had  been  subjected.  The  whole  circumference  of  the 
earth  is  but  25,000  miles,  so  that  this  wave  had  trav- 
elled over  a  distance  considerably  greater  than  two- 
fifths  of  the  earth's  circumference.  A  distance  which 
the  swiftest  of  our  ships  could  not  traverse  in  less  than 
six  or  seven  weeks  had  been  swept  over  by  this  enor- 
mous undulation  in  the  course  of  a  few  hours. 

More  complete  details  reach  us  from  the  Southern 
Pacific. 


228  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

Shortly  before  midnight  the  Marquesas  Isles  and 
the  low-lying  Tuamotu  group  were  visited  "by  the 
great  wave,  and  some  of  these  islands  were  completely 
submerged  by  it.  The  lonely  Opara  Isle,  where  the 
steamers  which  run  between  Panama  and  New  Zealand 
have  their  coaling-station,  was  visited  at  about  half- 
past  eleven  in  the  evening  by  a  billow  which  swept 
away  a  portion  of  the  coal-depot.  Afterward  great 
waves  came  rolling  in  at  intervals  of  about  twenty 
minutes,  and  several  days  elapsed  before  the  sea  re- 
sumed its  ordinary  ebb  and  flow. 

It  was  not  until  about  half-past  two  on  the  morning 
of  August  14th,  that  the  Samoa  Isles  (sometimes  called 
the  Navigator  Islands)  were  visited  by  the  great  wave. 
The  watchmen  startled  the  inhabitants  from  their  sleep 
by  the  cry  that  the  sea  was  about  to  overwhelm  them ; 
and  already,  when  the  terrified  people  rushed  from 
their  houses,  the  sea  was  found  to  have  risen  far  above 
the  highest  water-mark.  But  it  presently  began  to 
sink  again,  and  then  commenced  a  series  of  oscillations, 
which  lasted  for  several  days,  and  were  of  a  very  re- 
markable nature.  Once  in  every  quarter  of  an  hour 
the  sea  rose  and  fell,  but  it  was  noticed  that  it  rose 
twice  as  rapidly  as  it  sank.  This  peculiarity  is  well 
worth  remarking.  The  eminent  physicist  Mallet 
speaks  thus  (we  follow  Lyell's  quotation)  about  the 
waves  which  traverse  an  open  sea :  "  The  great  sea- 
wave,  advancing  at  the  rate  of  several  miles  in  a 


A  GREAT  SEA-WAVE.  229 

minute,  consists,  in  the  deep  ocean,  of  a  long,  low 
swell  of  enormous  volume,  having  an  equal  slope 
before  and  behind,  and  that  so  gentle  that  it  might 
pass  under  a  ship  without  being  noticed.  But  when  it 
reaches  the  edge  of  soundings,  its  front  slope  becomes 
short  and  steep,  while  its  rear  slope  is  long  and  gentle." 
On  the  shores  visited  by  such  a  wave,  the  sea  would 
appear  to  rise  more  rapidly  than  it  sank.  "We  have 
seen  that  this  happened  on  the  shores  of  the  Samoa 
group,  and  therefore  the  way  in  which  the  sea  rose 
and  fell  on  the  days  following  the  great  earthquake 
gave  significant  evidence  of  the  nature  of  the  sea-- 
bottom  in  the  neighborhood  of  these  islands.  As 
the  change  of  the  great  wave's  figure  could  not  have 
been  quickly  communicated,  we  may  conclude  with 
certainty  that  the  Samoan  Islands  are  the  summits  of 
lofty  mountains,  whose  sloping  sides  extend  far  toward 
the  east. 

This  conclusion  affords  interesting  evidence  of  the 
necessity  of  observing  even  the  seemingly  trifling  de- 
tails of  important  phenomena. 

The  wave  which  visited  the  New-Zealand  Isles  was 
altogether  different  in  character,  affording  a  note- 
worthy illustration  of  another  remark  of  Mallet's.  He 
says  that  where  the  sea-bottom  slopes  in  such  a  way 
that  there  is  water  of  some  depth  close  in-shore,  the 
great  wave  may  roll  in  and  do  little  damage ;  and  we 
have  seen  that  so  it  happened  in  the  case  of  the 


230  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

Samoan  Islands.  But  he  adds,  that  "  where  the  shore 
is  shelving,  there  will  be  first  a  retreat  of  the  water, 
and  then  the  wave  will  break  upon  the  beach  and  roll 
far  in  upon  the  land."  This  is  precisely  what  happened 
when  the  great  wave  reached  the  eastern  shores  of 
New  Zealand,  which  are  known  to  shelve  down  to 
very  shallow  water  continuing  far  away  to  sea  toward 
the  east. 

At  about  half- past  three  on  the  morning  of  August 
14th,  the  water  began  to  retreat  in  a  singular  manner 
from  the  port  of  Littleton,  on  the  eastern  shores  of  the 
southernmost  of  the  New-Zealand  Islands.  At  length 
the  whole  port  was  left  entirely  dry,  and  so  remained 
for  about  twenty  minutes.  Then  the  water  was  seen 
returning  like  a  wall  of  foam  ten  or  twelve  feet  in 
height,  which  rushed  with  a  tremendous  noise  upon 
the  port  and  town.  Toward  five  o'clock  the  water 
again  retired,  very  slowly  as  before,  not  reaching  its 
lowest  ebb  until  six.  An  hour  later,  a  second  huge 
wave  inundated  the  port.  Four,  times  the  sea  retired 
and  returned  with  great  power  at  intervals  of  about  two 
hours.  Afterward  the  oscillation  of  the  water  was 
less  considerable,  but  it  had  not  wholly  ceased  until 
August  17th,  and  only  on  the  18th  did  the  regular  ebb 
and  flow  of  the  tide  recommence. 

Around  the  Samoa  group  the  water  rose  and  fell 
once  in  every  fifteen  minutes,  while  on  the  shores  of 
New  Zealand  each  oscillation  lasted  no  less  than  two 


A  GREAT  SEA- WAVE.  231 

hours.  Doubtless  the  different  depths  of  water,  the 
irregular  conformation  of  the  island-groups,  and  other 
like  circumstances,  were  principally  concerned  in  pro- 
ducing these  singular  variations.  Yet  they  do  not 
seem  fully  sufficient  to  account  for  so  wide  a  range  of 
difference.  Possibly  a  cause  yet  unnoticed  may  have 
had  something  to  do  with  the  peculiarity.  In  waves 
of  such  enormous  extent,  it  would  be  quite  impossible 
to  determine  whether  the  course  of  the  wave-motion 
was  directed  full  upon  a  line  of  shore  or  more  or  less 
obliquely.  It  is  clear  that  in  the  former  case  the 
waves  would  seem  to  follow  each  other  more  swiftly 
than  in  the  latter,  even  though  there  were  no  difference 
in  their  velocity. 

Far  on  beyond  the  shores  of  New  Zealand  the  great 
wave  coursed,  reaching  at  length  the  coast  of  Australia. 
At  dawn  of  August  14th,  Moreton  Bay  was  visited  by 
five  well-marked  waves.  At  Newcastle,  on  the  Hunter 
Kiver,  the  sea  rose  and  fell  several  times  in  a  remark- 
able manner,  the  oscillatory  motion  commencing  at 
half-past  six  in  the  morning.  But  the  most  significant 
evidence  of  the  extent  to  which  the  sea-wave  travelled 
in  this  direction  was  afforded  at  Port  Fairy,  Belfast, 
South  Victoria.  Here  the  oscillation  of  the  water  was 
distinctly  perceived  at  mid-day  on  August  14th ;  and 
yet,  to  reach  this  point,  the  sea-wave  must  not  only 
have  travelled  on  a  circuitous  course  nearly  equal  in 
length  to  half  the  circumference  of  the  earth,  but  must 


232  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

have  passed  tlirongli  Bass's  Straits,  between  Australia 
and  Yan  Diemen's  Land,  and  so  have  lost  a  considera- 
ble portion  of  its  force  and  dimensions.  When  we  re- 
member that  had  not  the  effects  of  the  earth -shock  on 
the  water  been  limited  by  the  shores  of  South  America, 
a  wave  of  disturbance  equal  in  extent  to  that  which 
travelled  westward  would  have  swept  toward  the  east, 
we  see  that  the  force  of  the  shock  was  sufficient  to  have 
disturbed  the  waters  of  an  ocean  covering  the  whole 
surface  of  the  earth.  For  the  sea-waves  wrhich  reached 
Yokohama  in  one  direction  and  Port  Fairy  in  another 
had  each  traversed  a  distance  nearly  equal  to  half  the 
earth's  circumference ;  so  that  if  the  surface  of  the 
earth  were  all  sea,  waves  setting  out  in  opposite  direc- 
tions from  the  centre  of  disturbance  would  have  met 
each  other  at  the  antipodes  of  their  starting-point. 

It  is  impossible  to  contemplate  the  effects  which 
followed  the  great  earthquake — the  passage  of  a  sea- 
wave  of  enormous  volume  over  fully  one-third  of  the 
earth's  surface,  and  the  force  with  which,  on  the  far- 
thermost limits  of  its  range,  the  wave  rolled  in  upon 
shores  more  than  10,000  miles  from  its  starting-place — 
without  feeling  that  those  geologists  are  right  who 
deny  that  the  subterranean  forces  of  the  earth  are 
diminishing  in  intensity.  It  may  be  difficult,  perhaps, 
to  look  on  the  effects  which  are  ascribed  to  ancient 
earth-throes  without  imagining  for  a  while  that  the 
power  of  modern  earthquakes  is  altogether  less.  But 


THE  USEFULNESS  OF  EARTHQUAKES.  233 

when  we  consider  fairly  the  share  which  time  had  in 
those  ancient  processes  of  change,  when  we  see  that 
while  mountain-ranges  were  being  upheaved  or  valleys 
depressed  to  their  present  position,  race  after  race  and 
type  after  type  appeared  on  the  earth,  and  lived  out 
the  long  lives  which  belong  to  races  and  to  types,  we 
are  recalled  to  the  remembrance  of  the  great  work 
which  the  earth's  subterranean  forces  are  still  engaged 
upon.  Even  now,  continents  are  being  slowly  de- 
pressed or  upheaved ;  even  now  mountain-ranges  are 
being  raised  to  a  new  level,  table-lands  are  in  process 
of  formation,  and  great  valleys  are  being  gradually 
scooped  out.  It  may  need  an  occasional  outburst  such 
as  the  earthquake  of  August,  1868,  to  remind  us  that 
great  forces  are  at  work  beneath  the  earth's  surface. 
But,  in  reality,  the  signs  of  change  have  long  been 
noted.  Old  shore-lines  shift  their  place,  old  soundings 
vary ;  the  sea  advances  in  one  place  and  retires  in 
another ;  on  every  side  Nature's  plastic  hand  is  at 
work  modelling  and  remodelling  the  earth,  in  order 
that  it  may  always  be  a  fit  abode  for  those  who  are  to 
dwell  upon  it. 

(From  Fraser^s  Magazine,  July,  1870.) 


THE   USEFULNESS    OF  EARTHQUAKES. 


have  lately  had  fearful  evidence  of  the  energy 
of  the  earth's  internal  forces.     A  vibration  which, 


234  LIGHT   SCIENCE  FOR  LEISURE  HOURS. 

when  considered  with  reference  to  the  dimensions  of 
the  earth's  globe,  may  be  spoken  of  as  an  indefinitely 
minute  quivering  limited  to  an  insignificant  area,  has 
sufficed  to  destroy  the  cities  and  villages  of  whole  prov- 
inces, to  cause  the  death  of  thousands  of  human  beings, 
and  to  effect  a  destruction  of  property  which  must  be 
estimated  by  millions  of  pounds  sterling.  Such  a  ca- 
tastrophe as  this  serves  indeed  to  show  how  poor  and 
weak  a  creature  man  is  in  presence  of  the  grand  work- 
ings of  Nature.  The  mere  throes  which  accompany 
her  unseen  subterranean  efforts  suffice  to  crumble  man's 
strongest  buildings  in  a  moment  into  dust,  while  the 
unfortunate  inhabitants  are  either  crushed  to  death 
among  the  ruins,  or  forced  to  remain  shuddering  spec- 
tators of  the  destruction  of  their  homes. 

At  first  sight  it  may  seem  paradoxical  to  assert 
that  earthquakes,  fearfully  destructive  as  they  have 
so  often  proved,  are  yet  essentially  preservative  and 
restorative  phenomena;  yet  this  is  strictly  the  case. 
Had  no  earthquakes  taken  place  in  old  times,  man 
would  not  now  be  living  on  the  face  of  the  earth ;  if 
no  earthquakes  were  to  take  place  in  future,  the  term 
of  man's  existence  would  be  limited  within  a  range  of 
time  far  less  than  that  to  which  it  seems  likely,  in  all 
probability,  to  be  extended. 

If  the  solid  substance  of  the  earth  formed  a  perfect 
sphere  in  ante-geologic  times — that  is,  in  ages  preceding 
those  to  which  our  present  geologic  studies  extend — 


THE  USEFULNESS  OF  EARTHQUAKES.  235 

there  can  be  no  doubt  that  there  was  then  no  visible 
land  above  the  surface  of  the  water ;  the  ocean  must 
have  formed  a  uniformly  deep  covering  to  the  sub- 
merged surface  of  the  solid  globe.  In  this  state  of 
things,  nothing  but  the  earth's  subterranean  forces 
could  tend  to  the  production  of  continents  and  islands. 
Let  us  be  understood.  "We  are  not  referring  to  the 
possibility  or  impossibility  that  lands  and  seas  should 
suddenly  have  assumed  their  present  figure  without 
convulsion  of  any  sort ;  this  might  have  happened, 
since  the  Creator  of  all  things  can  doubtless  modify  all 
things  according  to  His  will ;  we  merely  say  that, 
assuming  that  in  the  beginning,  as  now,  He  permitted 
all  things  to  work  according  to  the  laws  He  has  ap- 
pointed, then,  undoubtedly,  the  submerged  earth  must 
have  risen  above  the  sea  by  the  action  of  those  very 
forms  of  force  which  produce  the  earthquake  in  our 
own  times. 

However  this  may  be,  it  is  quite  certain  that  when 
once  continents  and  islands  had  been  formed,  there 
immediately  began  a  struggle  between  destructive  and 
restorative  (rather,  perhaps,  than  preservative)  forces. 

The  great  enemy  of  the  land  is  water,  and  water 
works  the  destruction  of  the  land  in  two  principal 
ways. 

In  the  first  place,  the  sea  tends  to  destroy  the  land 
by  beating  on  its  shores,  and  thus  continually  washing 
it  away.  It  may  seem  at  first  sight  that  this  process 


230  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

must  necessarily  be  a  slow  one ;  in  fact,  many  may 
be  disposed  to  say  that  it  is  certainly  a  slow  process, 
since  we  see  that  it  does  not  alter  the  forms  of  conti- 
nents and  islands  perceptibly  in  long  intervals  of  time. 
But,  as  a  matter  of  fact,  we  have  never  had  an  oppor- 
tunity of  estimating  the  full  effects  of  this  cause,  since 
its  action  is  continually  being  checked  by  the  restora- 
tive forces  we  shall  presently  have  to  consider.  Were 
it  not  thus  checked,  there  can  be  little  doubt  that  its 
effects  would  be  cumulative ;  for  the  longer  the  process 
continued — that  is,  the  more  the  land  was  beaten 
away — the  higher  would  the  sea  rise,  and  the  greater 
power  would  it  have  to  effect  the  destruction  of  the 
remaining  land. 

We  proceed  to  give  a  few  instances  of  the  sea's 
power  of  effecting  the  rapid  destruction  of  the  land 
when  nothing  happens  to  interfere  with  the  local 
action — premising,  that  this  effect  is  altogether  insig- 
nificant in  comparison  with  that  which  would  take 
place,  even  in  that  particular  spot,  if  the  sea's  action 
were  everywhere  left  unchecked. 

The  Shetland  Isles  are  composed  of  substances 
which  seem,  of  all  others,  best  fitted  to  resist  the 
disintegrating  forces  of  the  sea  —  namely,  granite, 
gneiss,  mica-slate,  serpentine,  greenstone,  and  many 
other  forms  of  rock ;  yet,  exposed  as  these  islands  are 
to  the  uncontrolled  violence  of  the  Atlantic  Ocean, 
they  are  undergoing  a  process  of  destruction  which, 


THE  USEFULNESS  OF  EARTHQUAKES.  237 

even  within  historical  times,  has  produced  very  note- 
worthy changes.  "  Steep  cliffs  are  hollowed  out,"  says 
Sir  Charles  Lyell,  "into  deep  caves  and  lofty  arches; 
and  almost  every  promontory  ends  in  a  cluster  of 
rocks,  imitating  the  forms  of  columns,  pinnacles,  and 
obelisks."  Speaking  of  one  of  the  islands  of  this 
group,  Dr.  Hibbert  says :  "  The  isle  of  Stenness  pre- 
sents a  scene  of  unequalled  desolation.  In  stormy 
winters,  large  blocks  of  stone  are  overturned,  or  are 
removed  from  their  native  beds,  and  hurried  to  a 
distance  almost  incredible.  In  the  winter  of  1802,  a 
tabular  mass,  eight  feet  two  inches  by  seven  feet,  and 
five  feet  one  inch  thick,  was  dislodged  from  its  bed, 
and  carried  to  a  distance  of  from  eighty  to  ninety 
feet."  In  other  parts  of  the  Shetland  Isles,  where  the 
sea  has  encountered  less  solid  materials,  the  work  of 
destruction  has  proceeded  yet  more  effectively.  In 
Roeness,  for  example,  the  sea  has  wrought  its  way 
so  fiercely,  that  a  large  cavernous  aperture  250  feet 
long  has  been  hollowed  out.  "  But  the  most  sublime 
scene,"  says  Dr.  Hibbert,  "  is  where  a  rnural  pile  of 
porphyry,  escaping  the  process  of  disintegration  that 
is  devastating  the  coast,  appears  to  have  been  left  as 
a  sort  of  rampart  against  the  inroads  of  the  ocean. 
The  Atlantic,  when  provoked  by  wintry  gales,  batters 
against  it  with  all  the  force  of  real  artillery ;  and  the 
waves,  in  their  repeated  assaults,  have  at  length  forced 
for  themselves  an  entrance.  This  breach,  named  the 


238  LIGHT   SCIENCE  FOR  LEISURE  HOURS. 

Grind  of  the  Navir,  is  widened  every  winter  by  the 
overwhelming  surge  that,  finding  a  passage  through 
it,  separates  large  stones  from?  its  sides,  and  forces 
them  to  a  distance  of  no  less  than  180  feet.  In  two 
or  three  spots,  the  fragments  which  have  been  de- 
tached are  brought  together  in  immense  heaps,  that 
appear  as  an  accumulation  of  cubical  masses,  the  prod- 
uct of  some  quarry." 

Let  us  next  turn  to  a  portion  of  the  coast-line  of 
Great  Britain  which  is  neither  defended,  on  the  one 
hand,  by  barriers  of  rock,  nor  attacked,  on  the  other, 
by  the  full  fury  of  the  Atlantic  currents.  Along  the 
whole  coast  of  Yorkshire,  we  find  evidences  of  a  con- 
tinual process  of  dilapidation.  Between  the  projecting 
headland  of  Flamborough  and  Spurn  Point  (the  coast 
of  Holderness),  the  waste  is  particularly  rapid.  Many 
spots,  which  are  now  mere  sand-banks,  are  marked 
in  the  old  maps  of  Yorkshire  as  the  sites  of  ancient 
towns  and  villages.  Speaking  of  Hyde  (one  of  these), 
Pennant  says :  "  Only  the  tradition  is  left  of  this 
town."  Owthorne  and  its  church  have  been  for  the  most 
part  destroyed,  as  also  Auburn,  Hartburn,  and  Kilnsea. 
Mr.  Phillips,  in  his  "  Geology  of  Yorkshire,"  states 
that  not  unreasonable  fears  are  entertained  that,  at 
some  future  time,  Spurn  Point  itself  will  become  an 
island,  or  be  wholly  washed  away,  and  then  the  ocean, 
entering  into  the  estuary  of  the  Humber,  will  cause 
great  devastation.  Pennant  states  that  "  several  places, 


THE  USEFULNESS  OF  EARTHQUAKES.  239 

once  towns  of  note  upon  the  Humber,  are  now  only 
recorded  in  history ;  and  Ilavensperg  was  at  one  time 
a  rival  of  Hull,  and  a  port  so  very  considerable  in 
134:2,  that  Edward  Baliol  and  the  confederated  Eng- 
lish barons  sailed  from  hence  to  invade  Scotland ;  and 
Henry  IY.,  in  1399,  made  choice  of  this  port  to  land 
at,  to  effect  the  deposal  of  Richard  II. ;  yet  the  whole 
of  this  has  since  been  devoured  by  the  merciless 
ocean ;  extensive  sands,  dry  at  low  water,  are  to  be 
seen  in  their  stead."  The  same  writer  also  describes 
Spurn  Point  as  shaped  like  a  sickle,  and  the  land  to 
the  north,  he  says,  was  "  perpetually  preyed  on  by  the 
fury  of  the  German  Sea,  which  devours  whole  acres  at 
a  time." 

The  decay  of  the  shores  of  Norfolk  and  Suffolk 
is  also  remarkably  rapid.  Sir  Charles  Lyell  relates 
some  facts  which  throw  an  interesting  light  on  the 
ravages  which  the  sea  commits  upon  the  land  here. 
It  was  computed  that  when  a  certain  inn  was  built  at 
Sherringham,  seventy  years  would  pass  before  the  sea 
could  reach  the  spot ;  "  the  mean  loss  of  land  being 
calculated  from  previous  observations  to  be  somewhat 
less  than  one  yard  annually."  But  no  allowance  had 
been  made  for  the  fact  that  the  ground  sloped  from  the 
sea.  In  consequence  of  this  peculiarity,  the  waste  be- 
came greater  and  greater  every  year  as  the  cliff  grew 
lower.  "  Between  the  years  1824  and  1829,  no  less 
than  seventeen  yards  were  swept  away ; "  and  when 


240  LIGHT   SCIENCE  FOR  LEISURE  HOURS. 

Sir  Charles  Lyell  saw  the  place,  only  a  small  garden 
was  left  between  the  building  and  the  sea.  We  need 
hardly  add  that  all  vestiges  of  the  inn  have  long  since 
been  swept  away.  Lyell  also  relates  that,  in  1829, 
there  was  a  depth  of  water  sufficient  to  float  a  frigate 
at  a  point  where,  less  than  half  a  century  before,  there 
stood  a  cliff  fifty  feet  high  with  houses  upon  it. 

"We  have  selected  these  portions  of  the  coast  of 
Great  Britian,  not  because  the  destruction  of  our 
shores  is  greater  here  than  elsewhere,  but  as  serving  to 
illustrate  processes  of  waste  and  demolition  which  are 
going  on  around  all  the  shores,  not  merely  of  Great 
Britain,  but  of  every  country  on  the  face  of  the  earth. 
Here  and  there,  as  we  have  said,  there  are  instances  in 
which  a  contrary  process  seems  to  be  in  action.  Low- 
lying  banks  and  shoals  are  formed — sometimes  along 
stretches  of  coast  extending  for  a  considerable  distance. 
But  when  we  consider  these  formations  closely,  we  find 
that  they  rather  afford  evidence  of  the  energy  of  the 
destructive  forces  to  which  the  land  is  subject  than 
promise  to  make  up  for  the  land  which  has  been  swept 
away.  In  the  first  place,  every  part  of  these  banks 
consists  of  the  debris  of  other  coasts.  ISTow,  we  cannot 
doubt  that  of  earth  which  is  washed  away  from  our 
shores,  by  far  the  larger  part  finds  its  way  to  the  bot- 
tom of  the  deep  seas ;  a  small  proportion  only  can  be 
brought  (by  some  peculiarity  in  the  distribution  of 
ocean-currents,  or  in  the  progress  of  the  tidal  wave)  to 


THE   USEFULNESS   OF  EARTHQUAKES.  241 

aid  in  the  formation  of  shoals  and  banks.  The  larger, 
therefore,  such  shoals  and  banks  may  be,  the  larger 
must  be  the  amount  of  land  which  has  been  washed 
away  never  to  reappear.  And  although  banks  and 
shoals  of  this  sort  grow  year  by  year  larger  and 
larger,  yet  (unless  added  to  artificially)  they  continue 
always  either  beneath  the  surface  of  the  water,  in  the 
case  of  shoals,  or  but  very  slightly  raised  above  the 
surface.  Now,  if  we  suppose  the  destruction  of  land 
to  proceed  unchecked,  it  is  manifest  that  at  some 
period,  however  remote,  the  formation  of  shoals  and 
banks  must  come  to  an  end,  owing  to  the  continual 
diminution  of  the  land  from  the  demolition  of  which 
they  derive  their  substance.  In  the  mean  time,  the 
bed  of  the  sea  would  be  continually  filling  up,  the 
level  of  the  sea  would  be  continually  rising,  and 
thus  the  banks  would  either  be  wholly  submerged 
through  the  effect  of  this  cause  alone,  or  they  would 
have  so  slight  an  elevation  above  the  sea-level,  that  they 
would  offer  little  resistance  to  the  destructive  effects  of 
the  sea,  which  would  now  have  no  other  land  to  act  upon. 
Eut  we  have  yet  to  consider  the  second  principal 
cause  of  the  wasting  away  of  the  land.  The  cause  we 
have  just  been  dealing  with  acts  upon  the  shores  or 
outlines  of  islands  and  continents ;  the  one  we  have  now 
to  consider  acts  upon  their  interior.  It  will,  perhaps, 
hardly  be  supposed  that  the  fall  of  rain  upon  the  land 
could  have  any  appreciable  influence  in  the  demolition 

11 


242  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

of  continents ;  but  as  a  matter  of  fact,  there  are  few 
causes  to  which  geologists  are  disposed  to  ascribe  more 
importance.  The  very  fact  that  enormous  deltas  have 
been  formed  at  the  mouths  of  many  rivers — in  other 
words,  the  actual  growth  of  continents  through  the 
effects  of  rainfall — is  a  proof  how  largely  this  cause 
must  tend  to  destroy  and  disintegrate  the  interiors  of 
our  continents.  Dwelling  on  this  point,  Sir  Charles 
Lyell  presents  the  following  remarkable  illustration : 
"  During  a  tour  in  Spain,"  he  writes,  "  I  was  surprised 
to  see  a  district  of  gently-undulating  ground  in  Cata- 
lonia, consisting  of  red  and  gray  sandstone,  and  in  some 
parts  of  red  marl,  almost  entirely  denuded  of  herbage ; 
while  the  roots  of  the  pines,  holm  oaks,  and  some  other 
trees,  were  half  exposed,  as  if  the  soil  had  been  washed 
away  by  a  flood.  Such  is  the  state  of  the  forests,  for 
example,  between  Oristo  and  Yich,  and  near  San 
Lorenzo.  But,  being  overtaken  by  a  violent  thunder- 
storm in  the  month  of  August,  I  saw  the  whole  surface, 
even  the  highest  levels  of  some  flat-topped  hills,  stream- 
ing with  mud,  while  on  every  declivity  the  devastation 
of  torrents  was  terrific.  The  peculiarities  in  the  phys- 
iognomy of  the  district  were  at  one  explained ;  and  I 
was  taught  that,  in  speculating  on  the  greater  effects 
which  the  direct  action  of  rain  may  once  have  produced 
on  the  surface  of  certain  parts  of  England,  we  need 
not  revert  to  periods  when  the  heat  of  the  climate  was 
tropical." 


THE  USEFULNESS  OF  EARTHQUAKES.  243 

Combining  the  effects  of  the  sea's  action  upon  the 
shores  of  continents,  and  of  the  action  of  rain  upon 
their  interior,  and  remembering  that  unless  the  process 
of  demolition  were  checked  in  some  way,  each  cause 
would  act  from  year  to  year  with  new  force — one 
through  the  effects  of  the  gradual  rise  of  the  sea-bed, 
and  the  other  through  the  effects  of  the  gradual  increase 
of  the  surface  of  ocean  exposed  to  the  vaporizing  action 
of  the  sun,  which  increase  would  necessarily  increase 
the  quantity  of  rain  yearly  precipitated  on  the  land — 
we  see  the  justice  of  the  opinion  expressed  by  Sir  John 
Herschel,  that,  "  had  the  primeval  world  been  con- 
structed as  it  now  exists,  time  enough  has  elapsed,  and 
force  enough  directed  to  that  end  has  been  in  activity, 
to  have  long  ago  destroyed  every  vestige  of  land" 

"We  see,  then,  the  necessity  that  exists  for  the  action 
of  some  restorative  or  preservative  force  sufficient  to 
counteract  the  effects  of  the  continuous  processes  of 
destruction  we  have  indicated  above.  If  we  consider, 
we  shall  see  that  the  destructive  forces  owe  their  effi- 
ciency to  their  levelling  action,  that  is,  to  their  influence 
in  reducing  the  solid  part  of  the  earth  to  the  figure  of 
a  perfect  sphere ;  therefore  the  form  of  force  which  is 
required  to  counteract  them  is  one  that  shall  tend  to 
produce  irregularities  in  the  surface-contour  of  the 
earth.  And  it  will  be  remarked  that,  although  up- 
heaval is  the  process  which  appears  at  first  sight  to  be 
the  only  effectual  remedy  to  the  levelling  action  of 


244  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

rains  and  ocean-currents,  yet  the  forcible  depression  of 
the  earth's  surface  may  prove  in  many  instances  yet 
more  effective,  since  it  may  serve  to  reduce  the  sea- 
level  in  other  places. 

ISTow,  the  earth's  subterranean  forces  serve  to  pro- 
duce the  very  effects  which  are  required  in  order  to 
counteract  the  continual  disintegration  of  the  shores 
and  interior  parts  of  continents.  In  the  first  place, 
their  action  is  not  distributed  with  any  approach  to 
uniformity  over  different  parts  of  the  earth's  crust,  and 
therefore  the  figure  they  tend  to  give  to  the  surface  of 
that  crust  is  not  that  of  a  perfect  sphere.  This,  of 
itself,  secures  the  uprising  of  some  parts  of  the  solid 
earth  above  the  sea-level.  But  this  is  not  all.  On  a 
comparison  of  the  various  effects  due  to  the  action  of 
subterranean  forces,  it  has  been  found  that  the  forces 
of  upheaval  act  (on  the  whole)  more  powerfully  under 
continents,  and  especially  under  the  shore-lines  of  con- 
tinents, while  the  forces  of  depression  act  most  power- 
fully (on  the  whole)  under  the  bed  of  the  ocean.  It  need 
hardly  be  said  that  whenever  the  earth  is  upheaved  in 
one  part,  it  must  be  depressed  somewhere  else.  Kot 
necessarily  at  the  same  instant,  it  should  be  remarked. 
The  process  of  upheaval  may  be  either  momentarily 
accompanied  by  a  corresponding  process  of  depression, 
or  the  latter  process  may  take  place  by  a  gradual 
action  of  the  elastic  powers  of  the  earth's  crust ;  but  in 
one  way  or  the  other,  the  balance  between  upheaval 


THE  USEFULNESS  OF  EARTHQUAKES.  245 

and  depression  must  be  restored.  Hence,  if  it  can  be 
shown  that  for  the  most  part  the  forces  of  upheaval  act 
underneath  the  land,  it  follows — though  we  may  not  be 
able  to  recognize  the  fact  by  obvious  visible  signs — 
that  processes  of  depression  are  taking  place  under- 
neath the  ocean.  Now,  active  volcanoes  mark  the 
centre  of  a  district  of  upheaval,  and  nearly  all  volca- 
noes are  found  near  the  sea.  It  seems  as  if  Nature 
had  provided  against  the  inroads  of  the  ocean  by  seat- 
ing the  earth's  upheaving  forces  just  where  they  are 
most  wanted. 

Even  in  earthquake  districts  which  have  no  active 
vent,  the  same  law  is  found  to  prevail.  It  is  supposed 
by  the  most  eminent  seismologists  that  earthquake  re- 
gions around  a  volcano,  and  earthquake  regions  appar- 
ently disconnected  form  any  outlet,  differ  only  in  this 
respect,  that  in  the  one  case  the  subterranean  forces 
have  had  sufficient  power  to  produce  the  phenomena  of 
eruption,  while  in  the  other  they  have  not.  In  "  earth- 
quakes," says  Humboldt,  "we  have  evidence  of  a  vol- 
cano-producing force ;  but  such  a  force,  as  universally 
diffused  as  the  internal  heat  of  the  globe,  and  proclaim- 
ing itself  everywhere,  rarely  acts  with  sufficient  energy 
to  produce  actual  eruptive  phenomena;  and  when  it 
does  so,  it  is  only  in  isolated  and  particular  places." 

Of  the  influence  of  the  earth's  subterranean  forces 
in  altering  the  level  of  the  land,  we  might  quote  many 
remarkable  instances,  but  considerations  of  space  com- 


246  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

pel  us  to  confine  ourselves  to  two  or  three.  The  slow 
processes  of  upheaval  or  depression  may,  perhaps,  seem 
less  immediately  referable  to  subterranean  action  than 
those  which  are  produced  during  the  progress  of  an 
actual  earthquake.  We  pass  over,  therefore,  such  phe- 
nomena as  the  gradual  uprising  of  Sweden,  the  slow 
sinking  of  Greenland,  and  (still  proceeding  westward) 
the  gradual  uprising  of  Nova  Scotia  and  the  shores  of 
Hudson's  Bay.  Eemarkable  and  suggestive  as  these 
phenomena  really  are,  and  indisputable  as  the  evidence 
is  on  which  they  rest,  they  will  probably  seem  much 
less  striking  to  our  readers  than  those  which  we  are 
now  about  to  quote. 

On  the  19th  of  November,  1822,  a  widely-felt  and 
destructive  earthquake  was  experienced  in  Chili.  On 
the  next  day,  it  was  noticed  for  the  first  time  that  a 
broad  line  of  sea-coast  had  been  deserted  by  the  sea 
for  more  than  one  hundred  miles.  A  large  part  of  this 
tract  was  covered  by  shell-fish,  which  soon  died,  and 
exhaled  the  most  offensive  effluvia.  Between  the  old 
low-water  mark  and  the  new  one,  the  fishermen  found 
burrowing  shells,  which  they  formerly  had  to  search 
for  amid  the  surf.  Rocks  some  way  out  to  sea  which 
had  formerly  been  covered,  were  now  dry  at  half  ebb- 
tide. 

Careful  measurements  showed  that  the  rise  of  the 
land  was  greater  at  some  distance  inshore  than  along 
the  beach.  The  water-course  of  a  mill  about  a  mile 


THE  USEFULNESS  OF  EARTHQUAKES.  247 

inland  from  the  sea  had  gained  a  fall  of  fourteen  inches 
in  little  more  than  a  hundred  yards.  At  Valparaiso, 
the  rise  was  three  feet ;  at  Quintero,  four  feet. 

In  February,  1835,  and  in  November,  1837,  a  large 
tract  of  Chili  was  similarly  shaken,  a  permanent  rise  of 
two  feet  following  the  former  earthquake,  and  a  rise  of 
eight  feet  the  latter. 

The  earthquake  which  took  place  at  Cutch  in  1819 
is  perhaps  in  some  respects  yet  more  remarkable.  In 
this  instance,  phenomena  of  subsidence,  as  well  as  phe- 
nomena of  upheaval,  were  witnessed.  The  estuary  of 
the  Indus,  which  had  long  been  closed  to  navigation — 
being,  in  fact,  only  a  foot  deep  at  ebb-tide,  and  never 
more  than  six  feet  at  flood — was  deepened  in  parts  to 
more  than  eighteen  feet  at  low  water.  The  fort  and 
village  of  Sindree  was  submerged,  only  the  tops  of 
houses  and  walls  being  visible  above  the  water.  But 
although  this  earthquake  seemed  thus  to  have  a  land- 
destroying  instead  of  a  land-creating  effect,  yet  the 
instances  of  upheaval  were,  even  in  this  case,  far  more 
remarkable  than  those  of  depression.  "Immediately 
after  the  shock,"  says  Sir  Charles  Lyell,  "  the  inhabit- 
ants of  Sindree  saw  at  a  distance  of  five  miles  and  a 
half  from  their  village  a  long,  elevated  mound,  where 
previously  there  had  been  a  low  and  perfectly  level 
plain.  To  this  uplifted  tract  they  gave  the  name  of 
Ullah-Bund,  or  the  '  Mound  of  God,'  to  distinguish  it 
from  several  artificial  dams  previously  thrown  across 


248  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

the  eastern  arm  of  the  Indus.  It  has  been  ascertained," 
he  adds,  "  that  this  new-raised  country  is  upward  of 
fifty  miles  in  length  from  east  to  west,  running  parallel 
to  the  line  of  subsidence  which  caused  the  grounds 
around  Sindree  to  be  flooded.  The  breadth  of  the  ele- 
vation is  conjectured  to  be  in  some  parts  sixteen  miles, 
and  its  greatest  ascertained  height  above  the  original 
level  of  the  delta  is  ten  feet — an  elevation  which  ap- 
pears to  the  eye  to  be  very  uniform  throughout." 

(From  Chambers' s  Journal,  November  7,  1868.) 


THE  FORCING  POWER    OF  RAIN. 

THEKE  is  an  old  proverb  which  implies  that  England 
need  never  fear  drought ;  and  we  have  had  clear  evi- 
dence this  year  that  an  exceptionally  dry  summer  is 
not  necessarily  followed  by  a  bad  harvest.  But  we 
believe  that  when  a  balance  is  carefully  struck  between 
the  good  and  the  evil  effects  resulting  from  excessive 
drought  in  England,  it  will  be  found  that  the  latter 
largely  prevail.  In  fact,  it  is  only  necessary  to  observe 
the  effects  which  have  followed  the  recent  wet  weather 
to  recognize  the  fact  that  rain  has  a  forcing  power,  the 
very  diminished  supply  of  which  at  the  due  season 
cannot  fail  to  have  seriously  injurious  effects.  In  va- 
rious parts  of  England  we  see  evidences  of  the  action 
of  such  a  power  during  the  present  autumn  in  the 


THE  FORCING  POWER  OF  RAIN.  249 

blossoming  of  trees,  in  the  flowering  of  primroses  and 
other  spring  plants,  in  rich  growths  of  fungi,  and  in 
various  other  ways.  It  cannot  be  doubted  that  there 
is  here  a  comparative  waste  of  powers,  which,  expended 
in  due  season,  would  have  produced  valuable  results. 

The  modern  theories  of  the  correlation  of  force 
suffice  to  show  how  enormous  a  loss  a  country  suffers 
when  there  is  a  failure  in  the  supply  of  rain,  or  when 
that  supply  comes  out  of  its  due  season.  "When  we 
consider  rain  in  connection  with  the  causes  to  which 
it  is  due,  we  begin  to  recognize  the  enormous  amount 
of  power  of  which  the  ordinary  rainfall  of  a  country  is 
the  representative;  and  we  can  well  understand  how 
it  is  that  u  the  clouds  drop  fatness  on  the  earth." 

The  sun's  heat  is,  of  course,  the  main  agent — we 
may  almost  say  the  only  agent — in  supplying  the  rain- 
fall of  a  country.  The  process  of  evaporation  carried 
on  over  large  portions  of  the  ocean's  surface  is  con- 
tinually storing  up  enormous  masses  of  water  in  the 
form  of  invisible  aqueous  vapor,  ready  to  be  trans- 
formed into  cloud,  then  wafted  for  hundreds  of  miles 
across  seas  and  continents,  to  be  finally  precipitated 
over  this  or  that  country,  according  to  the  conditions 
which  determine  the  downfall  of  rain.  These  processes 
do  not  appear,  at  first  sight,  indicative  of  any  very 
great  expenditure  of  force,  yet,  in  reality,  the  force- 
equivalent  of  the  rain-supply  of  England  alone  for  a 
single  year  is  something  positively  startling.  It  has 


250  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

been  calculated  that  the  amount  of  heat  required  to 
evaporate  a  quantity  of  water  which  would  cover  an 
area  of  100  miles  to  a  depth  of  one  inch  would  be  equal 
to  the  heat  which  would  be  produced  by  the  combus- 
tion of  half  a  million  tons  of  coals.  The  amount  of 
force  of  which  this  consumption  of  heat  would  be  the 
equivalent,  corresponds  to  that  which  would  be  required 
to  raise  a  weight  of  upward  of  one  thousand  millions 
of  tons  to  a  height  of  one  mile.  Now,  when  we  re- 
member that  the  area  of  Great  Britain  and  Ireland  is 
about  120,000  square  miles,  and  that  the  annual  rain- 
fall averages  about  25  inches,  we  see  that  the  force- 
equivalent  of  the  rainfall  is  enormous.  All  the  coal 
which  could  be  raised  from  our  English  coal-mines  in 
thousands  of  years  would  not  give  out  heat  enough  to 
produce  England's  rain-supply  for  a  single  year.  When 
to  this  consideration  we  add  the  circumstance  that  the 
force  of  rain  produces  bad  as  well  as  good  effects — the 
former  when  the  rain  falls  at  undue  seasons  or  in  an 
irregular  manner,  the  latter  only  when  the  rainfall  is 
distributed  in  the  usual  manner  among  the  seasons — 
we  see  that  an  important  loss  accrues  to  a  country  in 
such  exceptional  years  as  the  present. 

There  are  few  subjects  more  interesting  than  those 
depending  on  the  correlation  of  physical  forces  ;  and 
we  may  add  that  there  are  few  the  study  of  which  bears 
more  largely  on  questions  of  agricultural  and  commer- 
cial economy.  It  is  only  of  late  years  that  the  silent 


THE  FORCING   POWER  OF  RAIN.  £61 

forces  of  Nature — forces  continually  in  action,  but 
which  are  too  apt  to  pass  unnoticed  and  unrecognized — 
have  taken  their  due  place  in  scientific  inquiry. 
Strangely  enough,  the  subject  has  been  found  to  have 
at  once  a  most  practical  bearing  on  business  relations, 
and  an  aspect  more  strikingly  poetical  than  any  other 
subject,  perhaps,  which  men  of  science  have  ever  taken 
in  hand  to  investigate.  "We  see  the  ordinary  processes 
of  Nature,  as  they  are  termed,  taking  their  place  in 
the  workshop  of  modern  wealth,  and  at  the  same  time 
exhibited  in  a  hundred  striking  and  interesting  physical 
relations.  What,  for  instance,  can  be  stranger  or  more 
poetical  than  the  contrast  which  Professor  Tyndall  has 
instituted  between  that  old  friend  to  the  agriculturist — 
the  wintry  snow-flake — and  the  wild  scenery  of  the 
Alps  ?  "I  have  seen,"  he  says,  "  the  wild  stone-ava- 
lanches of  the  Alps,  which  smoke  and  thunder  down 
the  declivities  .with  a  vehemence  almost  sufficient  to 
stun  the  observer.  I  have  also  seen  snow-flakes  de- 
scending so  softly  as  not  to  hurt  the  fragile  spangles 
of  which  they  were  composed ;  yet  to  produce  from 
aqueous  vapor  a  quantity  which  a  child  could  carry 
of  that  tender  material  demands  an  exertion  of  energy 
competent  to  gather  up  the  shattered  blocks  of  the 
largest  stone-avalanche  I  have  ever  seen,  and  pitch 
them  to  twice  the  height  from  which  they  fell." 

We  may  point  out  in  this  place  the  important  con- 
nection which  exists  between  the  rainfall  of  a  country 


252  LIGHT   SCIENCE  FOR  LEISURE  HOURS. 

and  the  amount  of  forest-land.  "We  notice  that  in 
parts  of  America  attention  is  being  paid — with  mark- 
edly good  results — to  the  influence  of  forests  in  encour- 
aging rainfall.  We  have  here  an  instance  in  which 
cause  and  effect  are  interchangeable.  Rain  encourages 
the  growth  of  an  abundant  vegetation,  and  abundant 
vegetation  in  turn  aids  to  produce  a  state  of  the  super- 
incumbent atmosphere  which  encourages  the  precipita- 
tion of  rain.  The  consequence  is,  that  it  is  very  neces- 
sary to  check,  before  it  is  too  late,  the  processes  which 
lead  to  the  gradual  destruction  of  forests.  If  these 
processes  are  continued  until  the  climate  has  become 
excessively  dry,  it  is  almost  impossible  to  remedy  the 
mischief,  simply  because  the  want  of  moisture  is  de- 
structive to  the  trees  which  may  be  planted  to  encour- 
age rainfalls.  Thus,  there  are  few  processes  more 
difficult  (as  has  been  found  by  experience  in  parts  of 
Spain  and  elsewhere)  than  the  change  of  an  arid  region 
into  a  vegetation-covered  district.  In  fact,  if  the  region 
is  one  of  great  extent,  the  attempt  to  effect  such  a 
change  is  a  perfectly  hopeless  one.  On  the  other  hand, 
the  contrary  process — that  is,  the  attempt  to  change  a 
climate  which  is  too  moist  into  one  of  less  humidity — 
is  in  general  not  attended  with  much  difficulty.  A 
judicious  system  of  clearing  nearly  always  leads  to  the 
desired  result. 

The  dryness  of  the  past  year  has  not  been  due  to 
the  want  of  moisture  in  the  air,  nor  to  the  exceptionally 


THE  FORCING  POWER  OF  RAIN.  253 

unclouded  condition  of  our  skies.  We  believe  that, 
on  the  whole,  the  skies  have  been  rather  more  cloudy 
than  usual  this  year.  The  fact  that  so  little  dew  has 
fallen  is  a  sufficient  proof  that  the  nights  have  been  on 
the  whole  more  cloudy  than  usual,  since,  as  is  well 
known,  the  presence  of  clouds,  by  checking  the  radia- 
tion of  the  earth's  heat,  prevents  (or  at  least  diminishes) 
the  formation  of  dew.  The  fact  would  seem  to  be  that 
the  westerly  and  southwesterly  winds  which  usually 
blow  over  England  during  a  considerable  part  of  the 
year,  bringing  with  them  large  quantities  of  aqueous 
vapor  from  above  the  great  Gulf  Stream,  have  this 
year  blown  somewhat  higher  than  usual.  "Why  this 
should  be  it  is  not  very  easy  to  say.  The  height  of 
the  vapor-laden,  winds  is  usually  supposed  to  depend 
on  the  heat  of  the  weather.  In  summer,  for  instance, 
the  clouds  range  higher,  and  therefore  travel  farther 
inland  before  they  fall  in  rain.  In  winter,  on  the  con- 
trary, they  travel  lower,  and  hence  the  rain  falls  more 
freely  in  the  western  than  in  the  eastern  countries 
during  winter.  A  similar  relation  prevails  in  the 
Scandinavian  peninsula — Norway  receiving  more  rain 
in  winter  than  in  summer,  while  Sweden  receives  more 
rain  in  summer  than  in  the  winter.  But  this  summer 
the  rain-clouds  have  blown  so  much  higher  than  usual 
as  to  pass  beyond  England  altogether.  Possibly  we 
may  find  an  explanation  in  the  fact  that  before  reach- 
ing our  shores  at  all  the  clouds  were  relieved  by  heavy 


254  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

rainfalls — probably  due  to  some  exceptional  electrical 
relations — over  parts  of  the  Atlantic  Ocean.  It  is 
stated  that  the  steamships  from  America  this  summer 
were,  in  many  instances,  drenched  by  heavy  showers 
until  they  neared  the  coasts  of  England. 

(From  the  Daily  Neivs,  October  o,  1868.) 


A   SHOWER    OF  SNOW-CRYSTALS. 

YESTEKDAY  morning  a  remarkably  fine  fall  of  snow* 
stars  took  place  over  many  parts  of  London.  The 
crystals  were  larger  and  more  perfectly  formed  than  is 
commonly  the  case  in  our  latitudes,  where  the  con- 
ditions requisite  for  the  formation  of  these  beautiful 
objects  are  less  perfectly  fulfilled  than  in  more  northerly 
regions.  Many  forms  were  to  be  noticed  which  the 
researches  of  Scoresby,  Glaisher,  and  Lowe,  have  shown 
to  be  somewhat  uncommon. 

Many  of  our  readers  will,  perhaps,  be  surprised  to 
learn  that  no  less  than  1,000  different  kinds  of  snow- 
crystals  have  been  noticed  by  the  observers  named 
above,  and  that  a  large  proportion  of  them  have  been 
figured  and  described.  The  patterns  are  of  wonderful 
beauty.  A  strange  circumstance  connected  with  these 
objects  is  the  fact  that  for  the  most  part  they  are 
found,  on  a  close  examination,  to  be  formed  of  minute 
colored  crystals  —  some  red,  some  green,  others  blue 


A  SHOWER  OF  SNOW-CRYSTALS,  255 

or  purple.  In  fact,  all  the  colors  of  the  rainbow  are 
to  be  seen  in  the  delicate  tracery  of  these  fine  hex- 
agonal stars.  So  that  in  the  perfect  whiteness  of  the 
driven  snow  we  have  an  illustration  of  the  well-known 
fact  that  the  colors  of  the  rainbow  combine  to  form 
the  purest  white.  For  the  common  snow-flake  is 
formed  of  a  large  number  of  such  tiny  crystals  as  were 
falling  yesterday ;  though  their  beauty  is  destroyed  in 
the  snow-flake,  through  the  effects  of  collision  and 
partial  melting.  It  may  not  be  very  commonly  known 
that  ordinary  ice,  also,  is  composed  of  a  combination 
of  crystals  presenting  all  the  regularity  of  formation 
seen  in  the  snow-crystals.  This  would  scarcely  be 
believed  by  any  one  who  examined  a  rough  mass  of 
ice  taken  from  the  surface  of  a  frozen  lake.  Yet,  if  a 
slice  be  cut  from  the  mass  and  placed  in  the  sun's 
light,  or  before  a  fire,  the  beautiful  phenomena  called 
ice-flowers  make  their  appearance — "  A  fairy  seems  to 
have  breathed  upon  the  ice,  and  caused  transparent 
flowers  of  exquisite  beauty  suddenly  to  blossom  in 
myriads  within  it." 

When  we  remember  that  the  enormous  ice-bergs 
of  the  Arctic  and  Antarctic  seas,  the  snow-caps  which 
crown  the  Alps,  and  Andes,  and  Himalayas,  and  the 
glaciers  which  urge  their  way  with  resistless  force 
down  the  mountain  valleys,  are  all  made  up  of  these 
delicate  and  beautiful  snow-flowers,  we  are  struck  with 
the  force  of  the  strange  contrasts  which  Nature  pre- 


250  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

Bents  to  our  contemplation.  "We  may  say  of  tlie  snow- 
crystals  what  Tennyson  said  of  the  small  sea-shell. 
Each  snow-star  is 

"Frail,  but  a  work  divine, 
Made  so  fairily  well, 
So  exquisitely  minute, 
A  miracle  of  design." 

Yet — massed  together  with  all  the  prodigality  of  Na- 
ture's unsparing  hand — they  crown  the  everlasting 
hills ;  or,  falling  in  avalanche  and  glacier,  overwhelm 
the  stoutest  works  of  man ;  or,  in  vast  islands  of  float- 
ing ice,  show  themselves  to  be 

"Offeree  to  withstand,  year  upon  year,  the  shock 
Of  cataract  seas  that  snap  the  three-decker's  oaken  spine." 

(From  the  Daily  News,  March  11,  18G9.) 


LONG   SHOTS. 

OUK  artillerists  have  paid  more  attention  of  late 
years  to  the  destructive  properties  of  various  forms  of 
cannon  than  to  the  question  of  range.  It  was  different 
when  first  the  rifling  of  cannon  was  under  discussion. 
Then  the  subject  which  was  most  attentively  con- 
sidered (after  accuracy  of  fire)  was  the  range  which 
might  possibly  be  obtained  by  various  improvements  in 
the  structure  of  rifled  cannon.  Many  of  our  readers 
will  remember  how,  soon  after  the  construction  of 


LONG  SHOTS.  257 

Armstrong  guns  had  been  commenced  in  the  Govern- 
ment factories,  a  story  was  spread  abroad  of  the 
wonderful  practice  which  had  been  made  with  this  gun 
at  a  range  of  seven  miles.  At  that  tremendous  range, 
a  shot  had  been  fired  into  the  middle  of  a  flock  of 
geese,  according  to  one  version  of  the  story ;  but  this 
was  presently  improved  upon,  and  we  were  told  that  a 
bird  had  been  singled  out  of  the  flock  by  the  artillerists 
and  successfully  "  potted !  "  Many  believed  this  little 
narrative;  though  some  few,  influenced  perhaps  by  the 
consideration  that  a  flock  of  geese  would  not  be  visible 
at  a  distance  of  seven  miles,  were  obstinately  in- 
credulous. Presently  it  turned  out  that  the  Arm- 
strong gun  was  incapable  of  throwing  a  shot  to  a 
distance  of  seven  miles ;  so  that  a  certain  air  of 
improbability  has  since  attached  to  the  narrative. 
Still  there  were  not  wanting  those  who  referred  to 
"  Queen  Anne's  pocket-pistol " — the  cannon  which  was 
able  to  throw  shot  across  the  Straits  of  Dover ;  and  in 
the  fulness  of  their  faith  in  that  mythical  piece  of 
ordnance,  they  refused  to  believe  that  the  skill  of 
modern  artillerists  was  unequal  to  the  construction  of 
cannon  even  more  effective. 

If  there  are  any  who  still  believe  in  the  powers 
ascribed  to  the  far-famed  "  pocket-pistol,"  they  will  find 
their  confidence  in  modern  artillery  largely  shaken  by 
the  announcement  that  it  is  considered  a  great  matter 
that  one  of  "Whitworth's  cannon  should  have  thrown  a 


258  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

shot  to  a  distance  of  very  nearly  six  and  a  half  miles. 
Not  only  is  this  so,  however,  but  it  is  well  known  that 
no  piece  of  ordnance  has  ever  flung  a  projectile  to  so 
great  a  distance  since  first  fire-arms  were  invented ;  and 
it  may  be  safely  predicted  that  men  will  never  be  able 
to  construct  a  cannon  which — as  far  as  range  is  con- 
cerned— will  do  much  better  than  this  one  of  Mr. 
Whitworth's.  The  greatest  range  which  had  ever  before 
been  obtained  fell  somewhat  short  of  six  miles.  The 
T-inch  steel  gun  contrived  by  Mr.  Lynall  Thomas  had 
flung  a*  projectile  weighing  one  hundred  and  seventy- 
five  pounds  to  a  distance  of  ten  thousand  and  seventy- 
five  yards  ;  and,  according  to  General  Lefroy's  "  Hand- 
book of  Artillery,"  that  was  the  greatest  range  ever 
recorded.  But  Mr.  Whitworth's  cannon  throws  a  shot 
more  than  a  thousand  yards  farther. 

Yery  few  have  any  idea  of  the  difficulties  which 
oppose  themselves  to  the  attainment  of  a  great  range 
in  artillery  practice.  It  may  seem,  at  first  sight,  the 
simplest  possible  matter  to  obtain  an  increase  of  range. 
Let  the  gun  be  made  but  strong  enough  to  bear  a  suffi- 
cient charge,  and  range  seems  to  be  merely  a  question 
of  the  quantity  of  powder  made  use  of.  But  in  reality 
the  matter  is  much  more  complicated.  The  artillerist 
has  to  contrive  that  the  whole  of  the  powder  made  use 
of  shall  be  burned  before  the  shot  leaves  the  cannon, 
and  yet  that  the  charge  shall  not  explode  so  rapidly  as 
to  burst  the  cannon.  If  he  used  some  forms  of  powder, 


LONG  SHOTS.  259 

very  useful  for  special  purposes,  half  the  charge  would 
be  blown  out  without  doing  its  share  of  work.  On  the 
other  hand,  there  are  some  combustibles — as  gun-cotton 
and  the  nitrates — which  burn  so  fast  that  the  gun 
would  be  likely  to  burst  before  the  shot  could  be  ex- 
pelled. Then,  again,  the  shot  must  fit  so  closely  that 
there  shall  be  no  windage,  and  yet  not  so  closely  as  to 
resist  too  much  the  action  of  the  exploding  powder. 
Again,  there  is  the  form  of  the  shot  to  be  considered. 
A  sphere  is  not  the  solid  which  passes  most  readily 
through  a  resisting  medium  like  the  air ;  and  yft,  other 
projectiles,  which  are  best  so  long  as  they  maintain  a 
certain  position,  meet  with  a  greater  resistance  when 
once  they  begin  to  move  unsteadily.  The  conoid  used 
in  ordinary  rifle-practice,  for  example,  passes  much 
more  freely  through  the  air,  point  first,  than  an  ordi- 
nary spherical  bullet ;  but  it  the  point  did  not  travel 
first,  as  would  happen  but  for  the  rifling,  or  even  if  the 
conoidal  bullet  "  swayed  about "  on  its  course,  it  would 
meet  with  more  resistance  than  a  spherical  bullet. 
Hence  the  question  of  "  fast  or  slow  rifling  "  has  to  be 
considered.  "  Fast  rifling  "  gives  the  greater  spin,  but 
causes  more  resistance  in  the  exit  of  the  shot  from 
the  barrel ;  with  "  slow  rifling,"  these  conditions  are 
reversed. 

And  then  the  common  notion  is  that  a  cannon-ball 
travels  in  the  crurve  called  a  parabola,  and  that  artil- 
lerists have  nothing  to  do  but  to  calculate  all  about 


260  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

this  parabola,  and  to  deduce  the  range  from  the  initial 
velocity  according  to  some  simple  principles  deduced 
from  the  properties  of  the  curve.  All  this  is  founded 
on  a  complete  misapprehension  of  the  true  difficulties 
in  the  way  of  the  problem.  Only  projectiles  thrown 
with  small  velocity  from  the  earth  travel  in  parabolic 
paths.  A  cannon-ball  follows  a  wholly  difierent  kind 
of  curve.  The  resistance  of  the  air,  which  seems  to 
most  persons  a  wholly  insignificant  item  in  the  in- 
quiry, is  so  enormous  in  the  case  of  a  cannon-ball  as  to 
become*  by  far  the  most  important  difficulty  in  the 
way  of  the  practical  artillerist.  "When  a  250-pound 
shot  is  hurled  with  such  force  from  a  gun  as  to  cover  a 
range  of  six  miles,  the  resistance  of  the  air  is  about 
forty  times  the  weight  of  the  ball — that  is,  is  equiva- 
lent to  a  weight  of  upward  of  four  tons.  The  range 
Is  such  a  case  as  this  is  but  a  small  fraction  of  that 
which  would  be  given  by  the  ordinary  parabolic 
theory. 

As  regards  artillery  practice  in  war,  there  are  other 
difficulties  in  the  attainment  of  a  very  extended  range. 
Cannon  meant  for  battering  down  forts  cannot  possibly 
be  used  in  the  same  way  that  "Whitworth's  was  used 
at  Shoeburyness.  If  the  shot  flung  from  this  gun  at 
an  elevation  of  thirty-three  degrees  could  have  been 
watched,  it  would  have  been  found  that  it  fell  to  the 
earth  at  a  much  greater  angle — that,  is,  much  more 
nearly  in  a  perpendicular  direction.  On  the  ordinary 


SHOTS.  201 

parabolic  theory,  of  course,  the  angle  of  fall  would  be 
the  same  as  the  angle  of  elevation,  but  under  actual 
circumstances  there  is  an  important  difference.  If 
forts  are  to  be  battered  down,  however,  it  will  not 
serve  that  they  should  be  struck  from  above;  our 
artillerists  must  perforce  keep  to  the  old  method  of 
pounding  away  at  the  face  of  the  forts  they  attack. 
Therefore,  an  elevation  which  is  all  very  well  for 
mortars — that  is,  when  the  question  merely  is  of  fling- 
ing a  bomb  into  a  town  or  fortress — is  utterly  unsuit- 
ed  for  ordinary  artillery.  With  an  elevation  of  10°, 
Whitworth's  cannon  scarcely  projected  the  250-lb. 
shot  to  a  distance  of  three  miles. 

The  progress  of  the  modern  science  of  gunnery  cer- 
tainly tends  to  increase  the  distance  at  which  armies 
will  engage  each  other.  "With  field  artillery  flinging 
shot  to  a  distance  of  two  or  three  miles,  and  riflemen 
able  to  make  tolerably  sure  practice  at  a  distance  of 
three-quarters  of  a  mile,  we  are  not  likely  often  to  hear 
of  hand-to-hand  conflicts  in  future  warfare.  The  use 
of  breech-loaders  will  also  tend  to  the  same  effect. 
Hitherto  we  have  scarcely  had  experience  of  the  re- 
sults which  these  changes  are  to  produce  on  modern 
warfare.  At  Sadowa  breech-loaders  did  not  encounter 
breech-loaders,  and  it  was  easy  for  the  victors  in  that 
battle  to  come  to  close  quarters  with  their  enemies. 
But  in  a  battle  where  both  sides  are  armed  with 
breech-loaders,  we  shall  probably  see  another  sort  of 


262  LIGHT   SCIENCE  FOR  LEISURE  HOURS. 

affair  altogether.  The  bayonet  will  be  an  almost  use- 
less addition  to  the  soldier's  arms  ;  a  charge  of  cavalry 
upon  well-armed  infantry  will  be  almost  as  hopeless 
as  the  famous  Balaklava  charge ;  and  the  artillery  on 
either  side  will  have  to  play  a  game  at  long  shots.  We 
venture  to  anticipate  that  the  first  great  European  war 
will  introduce  a  total  change  into  the  whole  system  of 
warlike  manoeuvres.* 

(From  the  Daily  News,  November,  1868.) 


INFLUENCE  OF  MARRIAGE  ON  THE  DEATH- 
RATE. 

THE  Koyal  Commission  on  the  Law  of  Marriage 
has  attracted  attention  to  many  singular  and  instruc- 
tive results  of  modern  statistical  inquiry.  ISTot  the 
least  important  of  these  is  the  apparent  influence  of 
marriage  on  the  death-rate.  For  several  years  it  has 
been  noticed  by  statisticians  that  the  death-rate  of  un- 
married men  is  considerably  higher  than  the  death-rate 
of  married  men  and  widowers.  "We  believe  that  Dr. 
Stark,  Registrar-General  for  Scotland,  was  one  of  the 
first  to  call  attention  to  this  peculiarity,  as  evidenced 
by  the  results  of  two  years'  returns  for  Scotland.  •  But 
the  law  has  since  been  confirmed  by  a  far  wider  range 
of  statistical  inquiry.  The  relative  proportion  between 

*  The  reader  need  hardly  be  reminded  of  the  most  complete  fulfil- 
ment of  this  anticipation. 


INFLUENCE   OF  MARRIAGE  ON  DEATH-RATE.        263 

the-  death-rates  of  the  married  and  of  the  unmarried  is 
not  absolutely  uniform  in  different  countries,  but  it  is 
fairly  enough  represented  by  the  following  table,  which 
exhibits  the  mortality  per  thousand  of  married  and  un- 
married men  in  Scotland : 


Ages. 

Husbands  and  Widowers. 

Unmarried. 

20  to  25 

6.26 

12.31 

25  to  30 

8.23 

14.94 

30  to  35 

8.65 

15.94 

35  to  40 

11.67 

16.02 

40  to  45 

14.07 

18.35 

45  to  50 

17.04 

21.18 

50  to  55 

19.54 

26.34 

55  to  60 

26.14 

*28.54 

60  to  65 

35.63 

44.54 

65  to  70 

62.93 

60.21 

70  to  75 

81.56 

102.71 

75  to  80 

117.85 

143.94 

80  to  85 

173.88 

195.40 

From  this  table  we  are  to  understand  that  out 
of  one  hundred  thousand  married  persons  (including 
widowers)  from  20  to  25  years  old,  626  die  in  the 
course  of  each  year;  while  out  of  a  similar  number 
of  unmarried  persons,  between  the  same  ages,  no  less 
than  1,231  die  in  each  year.  And  in  like  manner  all 
the  other  lines  of  the  table  are  to  be  interpreted. 

Commenting  on  the  evidence  supplied  by  the  above 
figures,  Dr.  Stark  stated  that  "  bachelorhood  is  more 
destructive  to  life  than  the  most  unwholesome  trades, 
or  than  residence  in  an  unwholesome  house  or  district, 


264  LIGHT   SCIENCE  FOR  LEISURE  HOURS. 

where  there  has  never  been  the  most  distant  attempt 
at  sanitary  improvement  of  any  kind."-  And  this  view 
has  been  very  generally  accepted,  not  only  by  the 
public,  but  by  professed  statisticians.  Yet  as  a  matter 
of  fact,  we  believe  that  no  such  inferences  can  legiti- 
mately be  drawn  from  the  above  table.  Dr.  Stark 
appears  to  us  to  have  fallen  into  the  mistake,  which 
M.  Quetelet  tells  us  is  so  common,  of  trying  to  make  his 
statistics  carry  more  weight  than  they  are  capable  of 
bearing.  It  is  important  that  the  matter  should  be 
put  in  a  just  light,  for  the  Royal  Commission  on  the 
Law  of  Marriage  has  revealed  no  more  striking  fact 
than  that  of  the  prevalence  of  immature  marriages, 
and  such  reasoning  as  Dr.  Stark's  certainly  cannot 
tend  to  discourage  these  unwise  alliances.  If  death 
strikes  down  in  five  years  only  half  as  many  of  those 
who  are  married  as  of  those  who  are  unmarried  be- 
tween the  age  of  20  and  25  (as  appears  from  the  above 
table),  and  if  the  proportion  of  deaths  between  the 
two  classes  goes  on  continually  diminishing  in  each 
successive  lustre  (as  is  also  shown  by  the  above  table), 
it  seems  reasonable  to  infer  that  the  death-rate  would 
be  even  more  strikingly  disproportionate  in  the  case 
of  persons  between  the  ages  of  fifteen  and  twenty  than 
in  the  case  of  persons  between  the  ages  of  twenty  and 
twenty-five.  "We  believe,  indeed,  that  if  Dr.  Stark 
had  extended  his  table  to  include  the  former  ages,  the 
result  would  have  been  such  as  we  have  indicated. 


INFLUENCE   OF  MARRIAGE   ON  DEATH-RATE.        265 

Yet  few  will  suppose  that  such  very  youthful  mar- 
riages can  exercise  so  singularly  beneficial  an  effect. 

To  many,  Dr.  Stark's  conclusion  may  appear  to  be 
a  natural  and  obvious  sequitur  from  the  evidence  upon 
which  it  is  founded.  Admitting  the  facts — and  we  see 
no  reason  for  doubting  them — it  may  appear  at  first 
sight  that  we  are  bound  to  accept  the  conclusion  that 
matrimony  is  favorable  to  longevity.  Yet  the  con- 
sideration of  a  few  parallel  cases  will  suffice  to  show 
how  small  a  foundation  the  figures  we  have  quoted 
supply  for  such  a  conclusion.  "What  would  be  thought, 
for  example,  of  any  of  the  following  inferences? 
Among  hot-house  plants  there  are  observed  a  greater 
variety  and  brilliancy  of  color  than  among  those  which 
are  kept  in  the  open  air,  therefore  the  housing  of 
plants  conduces  to  the  splendor  of  their  coloring.  Or 
again  :  The  average  height  of  Life  Guardsmen  is 
greater  than  that  of  the  rest  of  the  male  population, 
therefore  to  be  a  Life  Guardsman  conduces  to  tallness 
of  stature.  Or,  to  take  an  example  still  more  closely 
illustrative  of  Dr.  Stark's  reasoning — the  average  lon- 
gevity of  noblemen  exceeds  that  of  untitled  persons, 
therefore  to  have  a  title  is  conducive  to  longevity ;  or 
to  borrow  his  words,  "  to  remain  without  a  title  is  more 
destructive  to  life  than  the  most  unwholesome  trades, 
or  than  residence  in  an  unwholesome  house  or  district, 
where  there  has  never  been  the  most  distant  attempt 
at  sanitary  improvement  of  any  kind." 

12 


266  LIGHT   SCIENCE  FOIl   LEISURE   HOURS. 

We  know  that  tlie  inference  is  absurd  in  each  of 
the  above  instances,  and  we  are  able  at  once  to  show 
where  the  flaw  in  the  reasoning  lies.  We  know  that 
splendid  flowers  are  more  commonly  selected  for  hous- 
ing, and  that  Life  Guardsmen  are  chosen  for  their  tall- 
ness,  so  that  we  are  prevented  from  falling  into  the 
mistake  of  ascribing  splendor  of  color  in  the  one 
instance,  or  tallness  in  the  other,  to  the  influence  of 
causes  which  have  nothing  whatever  to  do  with  those 
attributes ;  nor  is  any  one  likely  to  ascribe  the  lon- 
gevity of  our  nobility  to  the  possession  of  a  title.  Yet 
there  is  nothing  in  any  one  of  the  above  inferences 
which  is  in  reality  more  unsound  than  Dr.  Stark's 
inference  from  the  mortality  bills,  when  the  latter  are 
considered  with  due  reference  to  the  principles  of  in- 
terpretation which  statisticians  are  bound  to  follow. 

The  fact  is,  that  in  dealing  with  statistics  the  utmost 
care  is  required  in  order  that  our  inferences  may  not 
be  pushed  beyond  the  evidence  afforded  by  our  facts. 
In  the  present  instance,  we  have  simply  to  deal  with 
the  fact  that  the  death-rate  of  unmarried  men  is 
higher  than  the  death-rate  of  married  men  and  widow- 
ers. From  this  fact  we  cannot  reason  as  Dr.  Stark 
lias  done  to  a  simple  conclusion.  All  that  we  can  do 
is  to  show  that  one  of  three  conclusions  must  be 
adopted-:  Either  matrimony  is  favorable  (directly  or 
indirectly)  to  longevity,  in  a  degree  sufficient  wholly 
to  account  for  the  observed  peculiarity ;  or  a  principle 


INFLUENCE   OF  MARRIAGE   ON  DEATH-RATE.        267 

of  selection — the  effect  of  which  is  such  as,  on  the 
whole,  to  fill  the  ranks  of  married  men-  from  among 
the  healthier  and  stronger  portion  of  the  community — 
operates  in  a  sufficient  degree  to  account  wholly  for 
the  observed  death-rates ;  or,  lastly,  the  observed  death- 
rates  are  due  to  the  combination,  in  some  unknown 
proportion,  of  the  two  causes  just  mentioned. 

E"o  reasonable  doubt  can  exist,  as  it  seems  to  us, 
that  the  third  is  the  true  conclusion  to  be  drawn  from 
the  evidence  supplied  by  the  mortality  bills.  Unfor- 
tunately, the  conclusion  thus  deduced  is  almost  value- 
less, because  we  are  left  wholly  in  doubt  as  to  the  pro- 
portion which  subsists  between  the  effects  to  be  ascribed 
to  the  two  causes  thus  shown  to  be  in  operation.  It 
scarcely  required  the  evidence  of  statistics  to  prove 
that  each  cause  must  operate  to  some  extent.  It  is 
perfectly  obvious,  on  the  one  hand,  that  although 
hundreds  of  men  who  would  be  held  by  insurance 
companies  to  be  "bad  lives"  may  contract  marriage, 
yet  on  the  whole  a  principle  of  selection  is  in  operation 
which  must  tend  to  bring  the  healthier  portion  of  the 
male  community  into  the  ranks  of  the  married,  and  to 
leave  the  unhealthier  in  the  state  of  bachelorhood.  A 
little  consideration  will  show  also  that,  on  the  whole, 
the  members  of  the  less  healthy  trades,  very  poor  per- 
sons, habitual  drunkards,  and  others  whose  prospects 
of  long  life  are  unfavorable,  must  (on  the  average  of 
a  large  number)  be  more  likely  to  remain  unmarried 


208  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

than  those  more  favorably  situated.  Another  fact 
drawn  from  the  Kegistrar-General's  returns  suffices  to 
prove  the  influence  of  poverty  on  the  marriage-rate. 
We  refer  to  the  fact  that  marriages  are  invariably 
more  numerous  in  seasons  of  prosperity  than  at  other 
times.  Improvident  marriages  are  undoubtedly  numer- 
ous, but  prosperity  and  adversity  have  their  influence, 
and  that  influence  not  unimportant,  on  the  marriage 
returns.  On  the  other  hand,  it  is  perfectly  obvious 
that  the  life  of  a  married  man  is  likely  to  be  more 
favorable  to  longevity  than  that  of  a  bachelor.  The 
mere  fact  that  a  man  has  a  wife  and  family  depending 
upon  him  will  suffice  to  render  him  more  careful  of  his 
health,  less  ready  to  undertake  dangerous  employ- 
ments, and  so  on  ;  and  there  are  other  reasons  which 
will  occur  to  every  one  for  considering  the  life  of  a 
married  men  better  (in  the  sense  of  the  insurance 
companies)  than  that  of  a  bachelor.  In  fact,  while 
we  are  compelled  to  reject  Dr.  Stark's  statement  that 
"  bachelorhood  is  more  destructive  to  life  than  the  most 
unwholesome  trades,  or  than  residence  in  an  unwhole- 
some house  or  district,  where  there  has  never  been  the 
most  distant  attempt  at  sanitary  improvement  of  any 
kind,"  we  may  safely  accept  his  opinion  that  statistics 
"  prove  the  truth  of  one  of  the  first  natural  laws  re- 
vealed to  man—'  It  is  not  good  that  man  should  live 
alone.'  "  "Whether  the  law  required  any  proof  is  a 
question  into  which  we  need  not  enter. 

(From  the  Daily  News,  October  17,  1868.) 


THE   TOPOGRAPHICAL  SURVEY  OF  INDIA.  269 


THE  TOPOGRAPHICAL  SURVEY  OF  INDIA. 

AT  the  close  of  the  war  with  Tippoo  Sahib,  Major 
Lambton  planned  the  triangulation  of  the  country 
lying  between  Madras  and  the  Malabar  coast,  a  dis- 
trict which  had  been  roughly  surveyed  during  the 
progress  of  the  war  by  Colonel  Mackenzie.  The 
Duke  of  Wellington  gave  his  approval  to  the  project, 
and  his  brother,  the  Governor-General  of  India,  and 
Lord  Olive  (son  of  the  great  Clive),  Governor  of  Ma- 
dras, used  their  influence  to  aid  Major  Lambton  in  car- 
rying out  his  design.  The  only  astronomical  instru- 
ment made  use  of  by  the  first  survey-party  was  one 
of  Eamsden's  zenith-sectors,  which  Lord  Macartney 
had  placed  in  the  hands  of  Dinwiddie,  the  astrono- 
mer, for  sale.  A  steel  chain,  which  had  been  sent 
with  Lord  Macartney's  embassy  to  the  Emperor  of 
China  and  refused,  was  the  only  apparatus  available 
for  measuring. 

Thus  began  the  Great  Trigonometrical  Survey  of 
India,  a  work  whose  importance  it  is  hardly  possible 
to  over-estimate.  Conducted  successively  by  Colonel 
Lambton,  Sir  George  Everest,  Sir  Andrew  Waugh, 
and  Lieutenant-Colonel  Walker  (the  present  superin- 
tendent), the  trigonometrical  survey  has  been  prose- 
cuted with  a  skill  and  accuracy  which  render  it  fairly 
comparable  with  the  best  works  of  European  sur- 


270  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

vejors.  But  to  complete  in  this  style  the  survey  of  the 
whole  of  India  would  be  the  work  of  several  centuries. 
The  trigonometrical  survey  of  Great  Britain  and  Ire- 
land has  been  already  more  than  a  century  in  progress, 
and  is  still  unfinished.  It  can,  therefore,  be  imagined 
that  the  survey  of  India — nearly  ten  times  the  size  of 
the  British  Isles,  and  presenting  difficulties  a  hundred- 
fold greater  than  those  which  the  surveyor  in  England 
has  to  encounter — is  not  a  work  which  can  be  quickly 
completed. 

But  the  growing  demands  of  the  public  service  have 
rendered  *it  imperatively  necessary  that  India  should 
be  rapidly  and  completely  surveyed.  This  necessity 
led  to  the  commencement  of  the  Topographical  Survey 
of  India,  a  work  which  has  been  pushed  forward  at  a 
surprising  rate  during  the  past  few  years.  Our  readers 
may  form  some  idea  of  the  energy  with  which  the  sur- 
vey is  in  progress  from  the  fact  that  Colonel  Thuillier's 
Report  for  the  season  1866-'6T  announces  the  charting 
of  an  area  half  as  large  as  Scotland,  and  the  prepara- 
tory triangulation  of  an  additional  area  nearly  half  as 
large  as  England. 

In  a  period  of  thirty  years,  with  but  few  surveying 
parties  at  first,  and  a  slow  increase  in  their  number,  an 
area  of  160,000  square  miles  has  been  completed  and 
mapped  by  the  topographical  department.  The  revenue 
surveyors  have  also  supplied  good  maps  (on  a  similar 
scale)  of  364^000  square  miles  of  country  during  the 


THE  TOPOGRAPHICAL  SURVEY  OF  INDIA.  271 

twenty  years  ending  in  1866.  Combining  these  results, 
we  have  an  area  of  524,000  square  miles,  or  upward  of 
four  times  that  of  Great  Britain  and  Ireland.  For  all 
this  enormous  area  the  surveyors  have  the  records  in  a 
methodical  and  systematic  form,  fit  for  incorporation  in 
the  atlas  of  India.  Nor  does  this  estimate  include  the 
older  revenue  surveys  of  the  northwestern  provinces, 
which,  for  want  of  proper  supervision  in  former  years, 
were  never  regularly  reduced.  The  records'  of  these 
surveys  were  destroyed  in  the  mutiny — chiefly  in  Haz- 
aumbaugh  and  the  southwestern  frontier  agency.  The 
whole  of  these  districts  remain  to  be  gone  over  in  a 
style  very  superior  to  that  of  the  last  survey. 

The  extent  of  the  country  which  has  been  charted 
may  lead  to  the  impression  that  the  survey  is  little  more 
than  a  hasty  reconnoissance.  This,  however,  is  very  far 
indeed  from  being  the  case.  The  preliminary  triangu- 
lation,  which  is  the  basis  of  the  topographical  survey,  is 
conducted  with  extreme  care.  In  the  present  Eeport, 
for  instance,  we  find  that  the  discrepancies  between  the 
common  sides  of  the  triangles — in  other  words,  the 
discrepancies  between  the  results  obtained  by  different 
observers — are  in  some  cases  less  than  one-tenth  of  an 
inch  per  mile ;  in  others  they  are  from  one  inch  to  a 
foot  per  mile ;  and  in  the  survey  of  the  Cossyah  and 
Garrow  Hills,  where  observations  had  to  be  taken  to 
large  objects  such  as  trees,  rocks,  etc.,  with  no  defined 
points  for  guidance,  the  results  differ  by  as  much  as 


272  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

twenty-six  inches  per  mile.  These  discrepancies  must 
not  only  be  regarded  as  insignificant  in  themselves,  but 
must  appear  yet  more  trifling  when  it  is  remembered 
that  they  are  not  cumulative,  inasmuch  as  the  prelim- 
inary triangulation  is  itself  dependent  on  the  great 
trigonometrical  survey. 

Let  us  understand  clearly  what  are  the  various  forms 
of  survey  which  are  or  have  been  in  progress  in  India. 
There  are  three  forms  to  be  considered  :  (1)  The  Great 
Trigonometrical  Surveys ;  (2)  The  Revenue  Surveys ; 
and  (3)  the  Topographical  Surveys. 

Great  trigonometrical  operations  are  extended  in  a 
straight  course  from  one  measured  base  to  another. 
Every  precaution  which  modern  skill  and  science  can 
suggest  is  taken  in  the  measurement  of  each  base-line, 
and  in  the  various  processes  by  which  the  survey  is 
extended  from  one  base-line  to  the  other.  The  accu- 
racy with  which  work  of  this  sort  is  conducted  may  be 
estimated  from  the  following  instance:  During  the 
progress  of  the  Ordnance  Survey  of  Great  Britain  and 
Ireland,  a  base-line  nearly  eight  miles  long  was  meas- 
ured near  Loch  Foyle  in  Ireland,  and  another  nearly 
seven  miles  long  on  Salisbury  Plain.  Trigonometrical 
operations  were  then  extended  from  Loch  Foyle  to 
Salisbury  Plain,  a  distance  of  about  340  miles ;  and 
the  Salisbury  base-line  was  calculated  from  the  obser- 
vations made  over  this  long  arc.  The  difference  'between 
the  measured  and  calculated  values  of  the  'base-line  was 


THE  TOPOGRAPHICAL  SURVEY  OF  INDIA.  273 

less  than  Jive  inches  !  As  we  have  stated,  the  trigono- 
metrical survey  of  India  will  bear  comparison  with  the 
best  work  of  our  surveyors  in  England. 

A  revenue  survey  is  prosecuted  for  the  definition 
of  the  boundaries  of  estates  and  properties.  The  op- 
erations of  such  a  survey  are  therefore  carried  on  con- 
formably to  those  boundaries. 

The  topographical  survey  of  a  country  is  defined  by 
Sir  A.  Scott  "Waugh  to  imply  "  the  measurement  and 
delineation  of  the  natural  features  of  a  country,  and 
the  works  of  man  thereon,  with  the  object  of  producing 
a  complete  and  sufficiently  accurate  map.  Being  free 
from  the  trammels  of  boundaries  of  properties,  the 
principal  lines  of  operations  must  conform  to  the  fea- 
tures of  the  country,  and  objects  to  be  surveyed." 

The  only  safe  basis  for  the  topographical  survey  of 
a  country  is  a  system  of  accurate  triangulation.  And 
where  the  extent  of  country  to  be  surveyed  is  large, 
there  will  always  be  a  great  risk  of  the  accumulation 
of  error  in  the  triangulation  itself ;  which  must  there- 
fore be  made  to  depend  on  the  accurate  results  obtained 
by  the  great  trigonometrical  operations.  In  order  to 
secure  this  result,  fixed  stations  are  established  in  the 
vicinity  of  the  great  trigonometrical  series.  Where 
this  plan  cannot  be  adopted,  a  net-work  of  large  sym- 
metrical triangles  is  thrown  over  the  district  to  be  sur- 
veyed, or  boundary  series  of  triangles  are  carried  along 
the  outline  of  the  district  or  along  convenient  internal 


274  LIGHT  SCIENCE  FOR  LEISURE  HOURS, 

lines.  The  former  of  these  methods  is  applicable  to  a 
hilly  district,  the  latter  to  a  flat  country. 

When  the  district  to  be  surveyed  has  been  triangu- 
lated, the  work  of  filling-in  the  topographical  details 
is  commenced.  Each  triangle  being  of  moderate  ex- 
tent, with  sides  from  three  to  five  miles  in  length,  and 
the  angular  points  being  determined,  as  we  have  seen, 
with  great  exactness,  it  is  evident  that  no  considerable 
error  can  occur  in  filling-in  the  details.  Hence,  methods 
can  be  adopted  in  the  final  topographical  work  which 
would  not  be  suitable  for  triangulation.  The  triangles 
can  either  be  "measured  up,"  or  the  observer  may 
traverse  from  trigonometrical  point  to  point,  taking 
offsets  and  intersections ;  or,  lastly,  he  may  make  use  of 
the  plane-table.  The  first  two  methods  require  little 
comment ;  but  the  principle  of  plane-tabling  enters  so 
largely  into  Indian  surveying,  that  our  notice  would  be 
incomplete  without  a  brief  account  of  this  simple  and 
beautiful  method. 

The  plane-table  is  a  flat  board  turning  on  a  verti- 
cal pivot.  It  bears  the  chart  on  which  the  observer  is 
planning  the  country.  Suppose,  now,  that  two  points 
A  and  B  are  determined,  and  that  we  require  to  mark 
in  the  position  of  a  third  point  c :  It  is  clear  that  if  we 
observed  with  a  theodolite  the  angles  ABC  and  B  A  c, 
we  might  lay  these  down  on  the  chart  with  a  protractor, 
and  so  the  position  of  c  would  be  determined  with  an 
accuracy  proportioned  to  the  care  with  which  the  ob- 


THE   TOPOGRAPHICAL  SURVEY  OF  INDIA.  275 

servations  were  made,  and  the  corresponding  construc- 
tions applied  to  the  chart.  But  in  "plane-tabling"  a 
more  direct  plan  is  adopted.  A  ruler  bearing  sights, 
resembling  those  of  a  rifle,  is  so  applied  that  the  edge 
passing  through  the  point  A  011  the  chart  (the  observer 
being  situated  at  the  real  station  A)  passes  through  the 
point  B  on  the  chart,  the  line  of  sight  passing  through 
the  real  station  B.  The  table  being  fixed  in  the  position 
thus  obtained,  the  ruler  is  next  directed  so  that  its  edge 
passes  through  A  while  the  line  of  sight  points  to  c.  A 
line  is  now  ruled  with  a  pencil  through  A  toward  c. 
In  a  similar  manner,  the  table  having  been  removed  to 
the  station  B,  a  pencil-line  is  drawn  through  the  point 
B  on  the  chart  toward  c.  The  two  lines  thus  drawn 
determine  by  their  intersection  the  place  of  c  on  the 
chart. 

The  above  is  only  one  instance  of  the  modes  in 
which  a  plane-table  can  be  applied ;  there  are  several 
others.  Usually  the  magnetic  compass  is  made  use  of 
to  fix  the  position  of  the  table  in  accordance  with  the 
true  bearing  of  the  cardinal  points.  Also  the  bearings 
of  several  points  are  taken  around  each  station ;  and 
thus  a  variety  of  tests  of  the  correctness  of  the  work 
become  applicable.  Into  such  points  as  these  we  need 
not  here  enter.  It  is  sufficient  that  our  readers  should 
have  been  enabled  to  gather  the  simple  principles  on 
which  plane-tabling  depends,  and  the  accuracy  with 
which  (when  suitable  precautions  are  taken)  it  can  be 


276  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

applied  as  a  method  of  observation  subsidiary  to  the 
ordinary  trigonometrical  processes. 

"  A  hilly  country,"  says  Sir  A.  Waugh,  "  offers  the 
fairest  field  for  the  practice  of  plane-table  surveys, 
and  the  more  rugged  the  surface  the  greater  will  be 
the  relative  advantages  and  facilities  this  system  pos- 
sesses over  the  methods  of  actual  measurement.  On 
the  other  hand,  in  flat  lands  the  plane-table  works  at 
a  disadvantage,  while  the  traverse  system  is  facilitated. 
Consequently,  in  such  tracts,  the  relative  economy  of 
the  two  systems  does  not  offer  so  great  a  contrast 
as  in  the  former.  In  closely-wooded  or  jungly  tracts, 
all  kinds  of  survey  operations  are  prosecuted  at  a 
disadvantage ;  but  in  such  localities,  the  commanding 
points  must  be  previously  cleared  for  trigonometrical 
operations,  which  facilitates  the  use  of  the  table." 

In  whatever  way  the  topographical  details  have 
been  filled-in,  a  rigorous  system  of  check  must  be 
applied  to  the  work.  The  system  adopted  is  that  of 
running  lines  across  ground  that  has  been  surveyed. 

This  is  done  by  the  head  of  the  party  or  by  the 
chief  assistant-surveyor.  A  sufficient  number  of  points 
are  obtained  in  this  way  for  comparison  with  the  work 
of  the  detail  surveyors ;  and  when  the  discrepancies 
exceed  certain  limits,  the  work  in  which  they  appear  is 
rejected.  Owing  to  the  extremely  unhealthy,  jungly, 
and  rugged  nature  o£  the  ground  in  which  nearly  all 
the  Indian  surveys  have  been  progressing,  it  has  not 


THE  TOPOGRAPHICAL  SURVEY  OF  INDIA.  277 

always  been  found  practicable  to  check  by  regularly 
chained  lines.  There  are,  however,  other  modes  of 
testing  plane-table  surveys,  and  as  these  entail  less 
labor  and  expense  in  hilly  and  jungly  tracts,  and  are 
quite  as  effective  if  thoroughly  carried  out,  they  have 
been  adopted  generally,  while  the  measured  routes  or 
check-lines  have  only  been  pursued  under  more  favor- 
able conditions.  Colonel  Thuillier  states  that  "the 
inspection  of  the  work  of  every  detailed  surveyor  in 
the  field  has  been  rigorously  enforced,  and  the  work  of 
the  field  season  is  not  considered  satisfactory  or  com- 
plete unless  this  duty  has  been  attended  to." 

The  rules  laid  down  to  insure  accuracy  in  the 
survey  are — first,  that  the  greatest  possible  number 
of  fixed  points  should  be  determined  by  regular  tri- 
angulation ;  secondly,  that  the  greatest  possible  num- 
ber of  plane-table  fixings  should  be  made  use  of 
within  each  triangle;  and,  lastly,  that  eye-sketching 
should  be  reduced  to  a  minimum.  If  these  rules  are 
well  attended  to,  the  surveyor  can  always  rely  on  the 
value  of  the  work  performed  by  his  subordinates. 
But  all  these  conditions  cannot  be  secured  in  many 
parts  of  the  ground  allotted  to  the  several  topographi- 
cal parties,  owing  to  the  quantity  of  forest-land  and 
the  extremely  rugged  nature  of  the  country.  Hence 
arises  the  necessity  for  test-lines  to  verify  the  details 
or  for  some  rigorous  system  of  check ;  and  this  is  more 
especially  the  case  where  native  agency  is  employed. 


278  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

So  soon  as  the  country  has  been  accurately  planned, 
the  configuration  of  the  ground  has  to  be  sketched  up. 
This  process  is  the  end  and  aim  of  all  the  preceding 
work. 

The  first  point  attended  to  is  the  arterial  system, 
or  water-drainage,  constituting  the  outfall  of  the 
country;  whence  are  deduced  the  lines  of  greatest 
depression  of  the  ground.  Next  the  water-sheds  or 
ridges  of  hills  are  traced  in,  giving  the  highest  level. 
Lastly,  the  minor  or  subordinate  features  are  drawn 
in  with  the  utmost  precision  attainable.  "  The  out- 
lines of  table-land  should  be  well  defined,"  says  Sir  A. 
Waugh,  "arid  ranges  of  hills  portrayed  with  fidelity, 
carefully  representing  the  water-sheds  or  divortia 
aquarum,  the  spurs,  peaks,  depressions  or  saddles, 
isthmuses  or  connecting-links  of  separate  ranges,  and 
other  ramifications.  The  depressed  points  and  isth- 
muses are  particularly  valuable,  as  being  either  the 
sites  of  ordinary  passes  or  points  which  new  roads 
should  conform  to." 

And  here  we  must  draw  a  distinction  between 
survey  and  reconnoissance.  It  is  absolutely  necessary 
in  making  a  survey  that  the  outlines  of  ground  as  de- 
fined by  ridges,  water-courses,  and  feet  of  hills,  should 
be  rigorously  fixed  by  actual  observation  and  careful 
measurement.  In  reconnoitring,  more  is  trusted  to 
the  eye. 

The  scale  of  the  Indian  topographical   survey  is 


THE   TOPOGRAPHICAL  SURVEY   OF  INDIA.  £79 

that  of  one  inch  per  mile ;  the  scale  of  half  an  inch 
per  mile  being  only  resorted  to  in  ^ery  densely-wooded 
or  jungly  country,  containing  few  inhabitants  and 
little  cultivated,  or  where  the  climate  is  so  dangerous 
that  it  is  desirable  to  accelerate  the  progress  of  the 
survey. 

On  the  scale  of  one  inch  per  mile  the  practised 
draughtsman  can  survey  about  five  square  miles  of 
average  country  per  day.  In  intricate  ground,  inter- 
sected by  ravines  or  covered  by  hills  of  irregular  for- 
mation, the  work  proceeds  much  more  slowly;  on 
the  other  hand,  in  open  and  nearly  level  country,  or 
where  the  hills  have  simple  outlines,  the  work  will 
cost  less  and  proceed  more  rapidly.  On  the  scale  of 
one  inch  per  mile  all  natural  features  (such  as  ravines 
or  water-courses)  more  than  a  quarter  of  a  mile  in 
length  can  be  clearly  represented.  Tillages,  towns, 
and  cities  can  be  shown,  with  their  principal  streets 
and  roads,  and  the  outlines  of  fortifications.  The 
general  figure  and  extent  of  cultivated,  waste,  and 
forest  lands,  can  be  delineated  with  more  or  less  pre- 
cision, according  to  their  extent.  Irrigated  rice-lands 
should  be  distinctly  indicated,  since  they  generally  ex- 
hibit the  contour  of  the  ground. 

The  relative  heights  of  hills  and  depths  of  valleys 
should  be  determined  during  the  course  of  a  topo- 
graphical survey.  These  vertical  elements  of  a  survey 
can  be  ascertained  by  trigonometrical  or  by  baro- 


280  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

metrical  observations,  or  by  a  combination  of  both 
methods.  "  The  barometer,"  says  Sir  A.  "Waugh,  "  is 
more  especially  useful  for  determining  the  level  of 
low  spots  from  which  the  principal  trigonometrical 
stations  are  invisible.  In  using  this  instrument,  how- 
ever, in  combination  with  the  other  operations,  the 
relative  differences  of  heights  are  to  be  considered 
the  quantities  sought,  so  that  all  the  results  may  be 
referable  to  the  original  trigonometrical  station.  The 
height  above  the  sea-level  of  all  points  coming  under 
any  of  the  following  heads  are  especially  to  be  deter- 
mined, for  the  purpose  of  illustrating  the  physical 
relief  of  the  country : 

"  1.  The  peaks  and  highest  points  of  ranges. 

"  2.  All  obligatory  points  required  for  engineer- 
ing works,  such  as  roads,  drainage,  and  irrigation, 
viz. :  the  highest  points  or  necks  of  valleys ;  the 
lowest  depressions  or  passes  in  ranges ;  the  junctions 
of  rivers,  and  debouchements  of  rivers  from  ranges ; 
the  height  of  inundation-level,  at  moderate  intervals 
of  about  three  miles  apart. 

"  3.  Principal  towns  or  places  of  note." 

Of  the  various  methods  employed  to  indicate  the 
steepness  of  slope,  that  of  eye-contouring  seems  alone 
to  merit  special  comment.  In  true  contouring,  regu- 
lar horizontal  lines,  at  fixed  vertical  intervals,  are 
traced  over  a  country,  and  plotted  on  to  the  maps. 
This  is  an  expensive  and  tedious  process,  whereas 


A  SHIP  ATTACKED  BY  A  SWORD-FISH.  281 

eye-contouring  is  easy,  light,  and  effective.  On  this 
system  all  that  is  necessary  is  that  the  surveyor 
should  consider  what  routes  persons  moving  horizon- 
tally would  pursue.  He  draws  lines  on  his  chart 
approximating  as  closely  as  possible  to  these  imagi- 
nary lines.  It  is  evident  that  when  lines  are  thus 
drawn  for  different  vertical  elevations,  the  resulting 
shading  will  be  dark  or  light,  according  as  the  slope  is 
steep  or  gentle.  This  method  of  shading  affords  scope 
as  well  for  surveying  skill  as  for  draughtsmanship. 

(From  Once  a  Week,  May  1,  1869.) 


A   SHIP  ATTACKED   BY  A   SWORD-FISH. 

WE  have  always  been  puzzled  to  imagine  how  the 
"  nine-and-twenty  knights  of  fame,"  described  in  the 
"  Lay  of  the  Last  Minstrel,"  managed  to  "  drink  the  red 
wine  through  the  helmet  barred."  But  in  Nature  we 
meet  with  animals  who  seem  almost  as  inconveniently 
armed  as  those  chosen  knights,  who 

.  .  .  "  quitted  not  their  armor  bright, 
Neither  by  day,  nor  yet  by  night." 

Among  such  animals  the  sword-fish  must  be  recog- 
nized as  one  of  the  most  uncomfortably-armed  crea- 
tures in  existence.  The  shark  has  to  turn  on  his  back 
before  he  can  eat,  and  the  attitude  scarcely  seems  sug- 
gestive of  a  comfortable  meal.  But  the  sword-fish  can 


282  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

hardly  even  by  that  arrangement  get  his  awkwardly- 
projecting  snout  out  of  the  way.  Yet  doubtless  this 
feature,  which  seems  so  inconvenient,  is  of  great  value 
to  Xiphias.  In  some  way  as  yet  unknown  it  enables 
him  to  get  his  living.  "Whether  he  first  kills  some  one 
of  his  neighbors  with  this  instrument,  and  then  eats 
him  at  his  leisure,  or  whether  he  plunges  it  deep  into 
the  larger  sort  of  fish,  and,  attaching  himself  to  them 
in  this  way,  sucks  nutriment  from  them  while  they 
are  yet  alive,  is  not  known  to  naturalists.  Certainly, 
he  is  fond  of  attacking  whales,  but  this  may  result 
not  so  much  from  gastronomic  tastes  as  from  a  natu- 
"ral  antipathy — envy,  perhaps,  at  their  superior  bulk. 
Unfortunately  for  himself,  Xiphias,  though  cold- 
blooded, seems  a  somewhat  warm-tempered  animal ; 
and,  when  he  is  angered,  he  makes  a  bull-like  rush 
upon  his  foe,  without  always  examining  with  due 
care  whether  he  is  likely  to  take  any  thing  by  his 
motion.  And  when  he  happens  to  select  for  attack  a 
stalwart  ship,  and  to  plunge  his  horny  beak  through 
thirteen  or  fourteen  inches  of  planking,  with  perhaps 
a  stout  copper  sheathing  outside  it,  he  is  apt  to  find 
some  little  difficulty  in  retreating.  The  affair  usually 
ends  by  his  leaving  his  sword  embedded  in  the  side 
of  the  ship.  In  fact,  no  instance  has  ever  been  re- 
corded of  a  sword-fish  recovering  his  weapon  (if  we 
may  use  the  expression)  after  making  a  lunge  of  this 
sort.  Last  Wednesday  the  Court  of  Common  Pleas — 


A  SHIP  ATTACKED  BY  A  SWORD-FISH.  283 

rather  a  strange  place,  by-the-by,  for  inquiring  into 
the  natural  history  of  fishes — was  engaged  for  several 
hours  in  trying  to  determine  under  what  circum- 
stances a  sword-fish  might  be  able  to  escape  scot-free 
after  thrusting  his  snout  into  the  side  of  a  ship.  The 
gallant  ship  "  Dreadnought,"  thoroughly  repaired, 
and  classed  A  1  at  Lloyd's,  had  been  insured  for 
£3,000  against  all  the  risks  of  the  seas.  She  sailed  on 
March  10,  1864-,  from  Colombo,  for  London.  Three 
days  later,  the  crew,  while  fishing,  hooked  a  sword- 
fish.  Xiphias,  however,  broke  the  line,  and  a  few 
moments  after  leaped  half  out  of  the  water,  with  the 
object,  it  should  seem,  of  taking  a  look  at  his  per- 
secutor, the  "Dreadnought."  Probably  he  satisfied 
himself  that  the  enemy  was  some  abnormally  large 
Cetacean,  which  it  was  his  natural  duty  to  attack 
forthwith.  Be  this  as  it  may,  the  attack  was  made, 
and  at  four  o'clock  the  next  morning  the  captain  was 
awakened  with  the  unwelcome  intelligence  that  the 
ship  had  sprung  a  leak.  She  was  taken  back  to  Co- 
lombo, and  thence  to  Cochin,  where  she  was  hove 
clown.  Near  the  keel  was  found  a  round  hole,  an 
inch  in  diameter,  running  completely  through  the 
copper  sheathing  and  planking. 

As  attacks  by  sword-fish  are  included  among  sea- 
risks,  the  insurance  company  was  willing  to  pay  the 
damages  claimed  by  the  owners  of  the  ship,  if  only  it 
could  be  proved  that  the  hole  had  really  been  made  by 


284  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

a  sword-fish.  No  instance  had  ever  been  recorded  in 
which  a  sword-fish  had  been  able  to  withdraw  his 
sword  after  attacking  a  ship.  A  defence  was  founded 
on  the  possibility  that  the  hole  had  been  made  in  some 
other  way.  Professor  Owen  and  Mr.  Frank  Buckland 
gave  their  evidence ;  but  neither  of  them  could  state 
quite  positively  whether  a  sword-fish  which  had  passed 
its  beak  through  three  inches  of  stout  planking  could 
withdraw  without  the  loss  of  its  sword.  Mr.  Buckland 
said  that  fish  have  no  power  of  "backing,"  and  ex- 
pressed his  belief  that  he  could  hold  a  sword-fish  by  the 
beak ;  but  then  he  admitted  that  the  fish  had  consider- 
able lateral  power,  and  might  so  "  wriggle  its  sword 
out  of  a  hole."  And  so  the  insurance  company  will 
have  to  pay  nearly  six  hundred  pounds  because  an  ill- 
tempered  fish  objected  to  be  hooked,  and  took  its 
revenge  by  running  full  tilt  against  copper-sheathing 
and  oak-planking. 

(From  the  Daily  News,  December  11,  1868.) 


THE   SAFETY-LAMP. 

As  the  late  colliery  explosions  have  attracted  a 
considerable  amount  of  attention  to  the  principle  of 
the  safety-lamp,  and  questions  have  arisen  respect- 
ing the  extent  of  the  immunity  which  the  action 
of  this  lamp  secures  to  the  miner,  it  may  be  well 


THE  SAFETY-LAMP.  285 

for  us  briefly  to  point   out  the  true  qualities  of  the 
lamp. 

In  the  Davy  lamp  a  common  oil-light  is  surrounded 
by  a  cylinder  of  wire-gauze.  When  the  air  around 
the  lamp  is  pure  the  flame  burns  as  usual,  and  the 
only  effect  of  the  gauze  is  somewhat  to  diminish  the 
amount  of  light  given  out  by  the  lamp.  But  so 
soon  as  the  air  becomes  loaded  with  the  carburetted 
hydrogen  gas  generated  in  the  coal-strata,  a  change 
takes  place.  The  flame  grows  larger  and  less  lumi- 
nous. The  reason  of  the  change  is  this :  The  flame 
is  no  longer  fed  by  the  oxygen  of  the  air,  but  is 
surrounded  by  an  atmosphere  which  is  partly  in- 
flammable ;  and  the  inflammable  part  of  the  gas,  so 
fast  as  it  passes  within  the  wire  cylinder,  is  ignited 
and  burns  within  the  gauze.  Thus  the  light  now 
given  out  by  the  lamp  is  no  longer  that  of  the  com- 
paratively brilliant  oil-flame,  but  is  the  light  resulting 
from  the  combustion  of  carburetted  hydrogen,  or 
"  fire-damp,"  as  it  is  called ;  and  every  student  of 
chemistry  is  aware  that  the  flame  of  this  gas  has  very 
little  illuminating  power. 

So  soon  as  the  miner  sees  the  flame  thus  enlarged 
and  altered  in  appearance,  he  should  retire.  But  it 
is  not  true  that  explosion  would  necessarily  follow  if 
he  did  not  do  so.  The  danger  is  great,  because  the 
flame  within  the  lamp  is  in  direct  contact  with  the 
gauze,  and  if  there  is  any  defect  in  the  wire-work, 


28G  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

the  lieat  may  make  for  itself  an  opening  which — 
though  small — would  yet  suffice  to  enable  the  flame 
writhin  the  lamp  to  ignite  the  gas  outside.  So  long, 
however,  as  the  wire-gauze  continues  perfect,  even 
though  it  become  red  hot,  there  will  be  no  explosion. 
No  authority  is  required  to  establish  this  point,  which 
has  been  proved  again  and  again  by  experiment ;  but 
we  quote  Professor  TyndalPs  words  on  the  subject 
to  remove  some  doubts  which  have  been  entertained 
on  the  matter :  "  Although  a  continuous  explosive  at- 
mosphere," he  says,  "  may  extend  from  the  air  outside 
through  the  meshes  of  the  gauze  to  the  flame  within, 
ignition  is  not  propagated  across  the  gauze.  The 
lamp  may  be  filled  with  an  almost  lightless  flame ; 
still  explosion  does  not  occur.  A  defect  in  the  gauze, 
the  destruction  of  the  wire  at  any  point  by  oxidation, 
hastened  by  the  flame  playing  against  it,  would  cause 
explosion; "  and  so  on.  It  need  hardly  be  said,  how- 
ever, that,  imprudent  as  miners  have  often  been,  no 
miner  would  remain  where  his  lamp  burned  with  the 
enlarged  flame  indicative  of  the  presence  of  fire- 
damp. The  lamp  should  also  be  at  once  extin- 
guished. 

But  here  we  touch  on  a  danger  which  undoubtedly 
exists,  and — so  far  as  has  yet  been  seen — cannot  be 
guarded  against  by  any  amount  of  caution.  Sup- 
posing the  miner  sought  to  extinguish  the  lamp  by 
blowing  it  out,  an  explosion  would  almost  certainly 


THE  SAFETY-LAMP.  287 

ensue,  since  the  flame  can.  be  forced  mechanically 
through  the  meshes,  though  it  will  not  pass  through 
them  when  it  is  burning  in  the  ordinary  way.  Now, 
of  course  no  miner  who  had  been  properly  instructed 
in  the  use  of  the  safety-lamp  would  commit  such  a 
mistake  as  this.  But  it  happens,  unfortunately,  that 
sometimes  the  fire-damp  itself  forces  the  flame  of  the 
lamp  through  the  meshes.  The  gas  frequently  issues 
with  great  force  from  cavities  in  the  coal  (in  which 
it  has  been  pent  up),  when  the  pick  of  the  miner 
breaks  an  opening  for  it.  In  these  circumstances  an 
explosion  is  inevitable,  if  the  issuing  stream  of  gas 
happen  to  be  directed  full  upon  the  lamp.  Fortu- 
nately,, however,  this  is  a  contingency  which  does  not 
often  arise.  It  is  one  of  those  risks  of  coal-mining 
which  seem  absolutely  unavoidable  by  any  amount  of 
care  or  caution.  It  would  be  well  if  it  were  only  such 
risks  as  these  that  the  miner  had  to  face. 

Another  peculiarity  sometimes  noticed  when  there 
is  a  discharge  of  fire-damp  is  worth  mentioning.  It 
happens,  occasionally,  that  the  light  will  be  put  out 
owing  to  the  absolute  exclusion  of  air  from  the  lamp. 
This,  however,  can  only  happen  when  the  gas  issues  in 
so  large  a  volume  that  the  atmosphere  of  the  pit  be- 
comes irrespirable. 

With  the  exception  of  the  one  risk  which  we  have 
pointed  out  above,  the  Davy  lamp  may  be  said  to  be 
absolutely  safe.  It  is  necessary,  however,  that  caution 


283  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

and  intelligence  should  Jbe  exhibited  in  its  use.  On 
this  point  Professor  Tyndall  remarks  that,  unfortu- 
nately the  requisite  intelligence  is  not  often  possessed 
nor  the  requisite  caution  exercised  by  the  miner,  "  and 
the  consequence  is  that,  even  with  the  safety-lamp, 
explosions  still  occur."  And  he  suggests  that  it  would 
be  well  to  exhibit  to  the  miner  in  a  series  of  experi- 
ments the  properties  of  the  valuable  instrument  which 
has  been  devised  for  his  security.  "  Mere  advice  will 
not  enforce  caution,"  he  says ;  "  but  let  the  miner  have 
the  physical  image  of  what  he  is  to  expect  clearly  and 
vividly  before  his  mind,  and  he  will  find  it  a  restrain- 
ing and  monitory  influence  long  after  the  effect  of 
cautioning  words  has  passed  away." 

A  few  words  on  the  history  of  the  invention  may 
be  acceptable.  Early  in  the  present  century  a  series 
of  terrible  catastrophes  in  coal-mines  had  excited  the 
sympathy  of  enlightened  and  humane  persons  through- 
out the  country.  In.  the  year  1813,  a  society  was 
formed  at  Sunderland  to  prevent  accidents  in  coal- 
mines, or  at  least  to  diminish  their  frequency,  and 
prizes  were  offered  for  the  discovery  of  new  methods 
of  lighting  and  ventilating  mines.  Dr.  "William  Reid 
Clanny,  of  Bishop wearmouth,  presented  to  this  society 
a  lamp  which  burned  without  explosion  in  an  atmos- 
phere heavily  loaded  with  fire-damp;  for  which  in- 
vention the  Society  of  Arts  awarded  him  a  gold  medal. 
The  Eev.  Dr.  Gray  called  the  attention  of  Sir  Humphry 


THE  SAFETY-LAMP.  289 

Davy  to  the  subject,  and  that  eminent  chemist  visited 
the  coal-mines  in  1815  with  the  object  of  determining 
what  form  of  lamp  would  be  best  suited  to  meet  the 
requirements  of  the  coal-miners.  He  invented  two 
forms  of  lamp  before  discovering  the  principle  on 
which  the  present  safety-lamps  are  constructed.  This 
principle — the  property,  namely,  that  flame  will  not 
pass  through  small  apertures— had  been,  we  believe, 
discovered  by  Stephenson,  the  celebrated  engineer, 
some  time  before  ;  and  a  somewhat  angry  controversy 
took  place  respecting  Davy's  claim  to  the  honor  of 
having  invented  the  safety-lamp.  It  seems  admitted, 
however,  by  universal  consent,  that  Davy's  discovery 
of  the  property  above  referred  to  was  made  indepen- 
dently, and  also  that  he  was  the  first  to  suggest  the 
idea  of  using  wire-gauze  in  place  of  perforated  tin. 

In  comparing  the  present  frequency  of  colliery  ex- 
plosions with  what  took  place  before  the  invention 
of  the  safety-lamp,  we  must  take  into  consideration 
the  enormous  increase  in  the  coal -trade  since  the 
introduction  of  steam  machinery.  The  number  of 
miners  now  engaged  in  our  coal-mines  is  far  in  ex- 
cess of  the  number  employed  in  the  beginning  of  the 
present  century.  Thus  accidents  in  the  present  day 
are  at  once  more  common  on  account  of  the  increased 
rapidity  with  which  the  mines  are  worked,  and  when 
they  occur  there  are  more  sufferers ;  so  that  the  fre- 
quency of  colliery  explosions  in  the  opening  years  of 

13 


290  LIGHT   SCIENCE  FOR  LEISURE  IIOURS. 

the  present  century,  and  the  number  of  deaths  result- 
ing from  them,  are  in  reality  much  more  significant 
than  th'ey  seem  to  be  at  first  sight.  But  even  inde- 
pendently of  this  consideration,  the  record  of  the 
colliery  accidents  which  took  place  at  that  time  is 
sufficiently  startling.  Seventy-two  persons  were  killed 
in  a  colliery  at  North  Biddick  at  the  commencement 
of  the  present  century.  Two  explosions  in  1805,  at 
Hepburn  and  Oxclose,  left  no  less  that  forty -three 
widows  and  a  hundred  and  fifty-one  children  unpro- 
vided for.  In  1808,  ninety  persons  were  killed  in  a 
coal-pit  at  Lumley.  On  May  24,  1812,  ninety-one 
persons  were  killed  by  an  explosion  at  Felling  Col- 
liery, near  Gateshead.  And  many  more  such  accidents 
might  readily  be  enumerated. 

(From  the  Daily  News,  December  4,  1868.) 


THE  DUST   WE  HAVE   TO   BREATHE. 

A  MICEOSCOPIST,  Mr.  Dancer,  F.  R.  A.  S.,  has  been 
examining  the  dust  of  our  cities.  The  results  are  not 
pleasing.  "We  had  always  recognized  city  dust  as  a 
nuisance,  and  had  supposed  that  it  derived  the  peculiar 
grittiness  and  flintiness  of  its  structure  from  the  con- 
stant macadamizing  of  city  roads.  But  it  now  appears 
that  the  effects  produced  by  dust,  when,  as  is  usual,  it 
fin  do  its  way  to  our  eyes,  our  nostrils,  and  our  throats, 


THE  DUST  WE  HAVE  TO  BREATHE.  291 

are  as  nothing  compared  with  the  mischief  it  is  calcu- 
lated to  produce  in  a  more  subtle  manner.  In  every 
specimen  examined  by  Mr.  Dancer,  animal  life  was 
abundant.  But  the  amount  of  "  molecular  activity  " — 
such  is  the  euphuism  under  which  what  is  exceedingly 
disagreeable  to  contemplate  is  spoken  about — is  vari- 
able according  to  the  height  at  which  the  dust  is 
collected.  And  of  all  heights  which  these  molecular 
wretches  could  select  for  the  display  of  their  activity, 
the'height  of  five  feet  is  that  which  lias  been  found  to 
be  the  favorite.  Just  at  the  average  height  of  the 
foot-passenger's  mouth  these  moving  organisms  are 
always  waiting  to  be  devoured  and  to  make  us  ill. 
And  this  is  not  all.  As  if  animal  abominations  were 
insufficient,  a  large  proportion  of  vegetable  matter 
also  disports  itself  in  the  light  dust  of  our  streets. 
The  observations  show  that  in  thoroughfares  where 
there  are  many  animals  engaged  in  the  traffic,  the 
greater  part  of  the  vegetable  matter  thus  floating  about 
"  consists  of  what  has  passed  through  the  stomachs  of 
animals,"  or  has  suffered  decomposition  in  some  way 
or  other.  This  unpleasing  matter,  like  the  "  molecular 
uctivity,"  floats  about  at  a  height  of  five  feet,  or  there- 
abouts. 

After  this,  one  begins  to  recognize  the  manner  in 
which  some  diseases  propagate  themselves.  "What  had 
been  mysterious  in  the  history  of  plagues  a,nd  pesti- 
lences seems  to  receive  at  least  a  partial  solution. 


292  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

Take  cholera,  for  example.  It  has  been  shown  by  the 
clearest  and  most  positive  evidence  that  this  disease  is 
not  propagated  in  any  way  save  one — that  is,  by  the 
actual  swallowing  of  the  cholera-poison.  In  Professor 
Thudichum's  masterly  paper  on  the  subject  in  the 
Monthly  Microscopical  Journal  it  is  stated  that  doc- 
tors have  inhaled  a  full  breathing  from  a  person  in 
the  last  stage  of  this  terrible  malady  without  any  evil 
effects.  Yet  the  minutest  atom  of  the  cholera-poison 
received  into  the  stomach  will  cause  an  attack  of  chol- 
era. A  small  quantity  of  this  matter  drying  on  the 
floor  of  the  patient's  room,  and  afterward  caused  to 
float  about  in  the  form  of  dust,  would  suffice  to  pros- 
trate a  houseful  of  people.  We  can  understand,  then, 
how  matter  might  be  flung  into  the  streets,  and,  after 
drying,  its  dust  be  wafted  through  a  whole  district, 
causing  the  death  of  hundreds.  One  of  the  lessons  to 
be  learned  from  these  interesting  researches  of  Mr. 
Dancer  is  clearly  this,  that  the  watering-cart  should 
be  regarded  as  one  of  the  most  important  of  our  hygi- 
enic institutions.  Supplemented  by  careful  scavenger- 
ing,  it  might  be  effective  in  dispossessing  many  a  ter- 
rible malady  which  now  holds  sway  from  time  to  time 
over  our  towns. 

(From  the  Daily  News,  March  6,  1869.) 


PHOTOGRAPHIC   GHOSTS.  293 


PHOTOGRAPHIC   GHOSTS. 

ON  the  outskirts  of  the  ever-widening  circle  lighted 
up  by  science  there  is  always  a  border-land  wherein  su- 
perstition holds  sway.  The  arts  and  sciences  may  drive 
away  the  vulgar  hobgoblin  of  darker  days  ;  but  they 
bring  with  them  new  sources  -of  illusion.  The  ghosts 
of  old  could  only  gibber ;  the  spirits  of  our  day  can 
read  and  write,  and  play  on  divers  instruments,  and 
quote  Shakespeare  and  Milton.  It  is  not,  therefore, 
altogether  surprising  to  learn  that  they  can  take  pho- 
tographs also.  You  go  to  have  your  photograph 
taken,  we  will  suppose,  desiring  only  to  see  your  own 
features  depicted  in  the  carte;  and  lo !  the  spirits  have 
been  at  work,  and  a  photographic  phantom  makes  its 
appearance  beside  you.  It  is  true  this  phantom  is  of  a 
hazy  and  dubious  aspect — the  "dull  mechanic  ghost" 
is  indistinct,  and  may  be  taken  for  any  one.  Still,  it 
is  not  difficult  for  the  eye  of  fancy  to  trace  in  it  the 
lineaments  of  some  departed  friend,  who,  it  is  to  be 
assumed,  has  come  to  be  photographed  along  with  you. 
In  fact,  photography,  according  to  the  spiritualist,  re- 
sembles what  Byron  called — 

"  The  lightning  of  the  mind, 
"Which,  out  of  things  familiar,  undesigned, 
When  least  we  deem  of  such,  calls  np  to  view 
The  spectres  whom  no  exorcism  can  bind." 

The  phenomena  of  spiritual  photography  were  first 


294  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

observed  some  years  since,  and  a  set  of  carte  photo: 
graphs  were  sent  from  America  to  Dr.  "Walker,  of 
Edinburgh,  in  which  photographic  phantoms  were  very 
obviously,  however  indistinctly,  discernible.  More 
recently  an  English  photographer  noticed  a  yet  stranger 
circumstance,  though  he  was  too  sensible  to  seek  for  a 
supernatural  interpretation  of  it.  "When  he  took  a 
photograph  with  a  particular  lens,  there  could  be  seen 
not  only  the  usual  portrait  of  the  sitter,  but  at  some 
little  distance  a  faint  "  double,"  exactly  resembling  the 
principal  image.  Superstitious  minds  might  find  this 
result  even  more  distressing  than  the  phantom  photo- 
graphic friend.  To  be  visited  by  the  departed  through 
the  medium  of  a  lens,  is  at  least  not  more  unpleasing 
than  to  hold  converse  with  spirits  through  an  ordi- 
nary "  rapping  "  medium.  But  the  appearance  of  a 
"double"  or  "fetch,"  has  ever  been  held  by  the 
learned  in  ghostly  lore  to  signify  approaching  death. 

Fortunately,  both  one  and  the  other  appearance  can 
be  very  easily  accounted  for  without  calling  in  the  aid 
of  the  supernatural.  At  a  recent  meeting  of  the  Pho- 
tographical  Society  it  was  shown  that  an  image  may 
often  be  so  deeply  impressed  on  the  glass  that  the  sub- 
sequent cleaning  of  the  plate,  even  with  strong  acids, 
will  not  completely  remove  the  picture.  "When  the 
plate  is  used  for  receiving  another  picture,  the  original 
image  makes  its  reappearance,  and  as  it  is  too  faint  to 
be  recognizable,  a  highly-susceptible  imagination  may 


OXFORD  AND  CAMBRIDGE  ROWING  STYLES.         295 

readily  transform  it  into  the  image  of  a  departed  friend. 
The  "  double  "  is  generated  by  the  well-known  property 
of  double  refraction,  obtained  by  a  lens  under  certain 
circumstances  of  unequal  pressure,  or  sometimes  by 
inequalities  in  the  process  of  annealing.  So  vanish 
two  ghosts  which  might  have  been  more  or  less 
troublesome  to  those  who  are  ready  to  see  the  super- 
natural in  commonplace  phenomena.  Will  the  time 
ever  come  when  no  more  such  phantoms  will  remain 
to  be  exorcised  ? 

(From  the  Daily  News,  March  2,  18G9.) 


THE  OXFORD  AND   CAMBRIDGE  ROWING 
STYLES. 

WHATEVER  opinion  we  may  have  of  the  result  of 
the  approaching  contest  (1869),  there  can  be  no  doubt 
that  this  year,  as  in  former  years,  there  is  a  striking 
dissimilarity  between  the  rowing  styles  of  the  dark- 
blue  and  the  light-blue  oarsmen.  This  dissimilarity 
makes  itself  obvious  whether  we  compare  the  two 
boats  as  seen  from  the  side,  or  when  the  line  of  sight 
is  directed  along  the  length  of  either.  Perhaps  it  is 
in  the  latter  aspect  that  an  unpractised  eye  will  most 
readily  detect  the  difference  we  are  speaking  of. 
Watch  the  Cambridge  boat  approaching  you  from 
some  distance,  or  receding,  and  you  will  notice  in  the 
rise  and  fall  of  the  oars,  as  so  seen,  the  following 


296  LIGHT  SCIENCE  FOR  LEISURE  HOURS, 

peculiarities — a  long'  stay  of  the  oar  in.  the  water,  a 
quick  rise  from  and  return  to  the  water,  the  oars 
remaining  out  of  the  water  for  the  briefest  possible 
interval  of  time.  In  the  case  of  the  Oxford  boat 
quite  a  different  appearance  is  presented — there  is  a 
short  stay  in  the  water,  a  sharp  rise  from  and  return 
to  it,  and  between  these  the  oars  appear  to  hang  over 
the  water  for  a  perceptible  interval.  It  is,  however, 
when  the  boats  are  seen  from  the  side  that  the 
meaning  of  these  peculiarities  is  detected,  and  also 
that  the  fundamental  distinction  between  the  two 
styles  is  made  apparent  to  the  experienced  eye.  In 
the  Cambridge  boat  we  recognize  the  long  stroke  and 
"  lightning  feather  "  inculcated  in  the  old  treatise  on 
rowing :  in  the  Oxford  boat  we  see  these  conditions 
reversed,  and  in  their  place  the  "  waiting  feather  "  and 
lightning  stroke.  By  the  "waiting  feather,"  we  do 
not  refer  to  what  is  commonly  understood  by  slow 
feathering,  but  to  a  momentary  pause  (scarcely  to  be 
detected  when  the  crew  is  rowing  hard)  before  the 
simultaneous  dash  of  the  oars  upon  the  first  grip  of 
the  stroke.*  And  observing  more  closely — which,  by- 
the-way,  is  no  easy  matter — as  either  boat  dashes 
swiftly  past,  we  detect  distinctive  peculiarities  of 
"  work  "  by  which  the  two  styles  are  severally  arrived 
at.  In  the  Cambridge  crew  we  see  the  first  part  of 

*  The  grip  is  never  properly  caught  without  the  pause ;  but  any  thing 
beyond  a  momentary  pause  is  a  bad  fault  in  style. 


OXFORD  AND   CAMBRIDGE   ROWING  STYLES.         297 

the  stroke  done  with  the  shoulders — precisely  accord- 
ing to  the  old- fashioned  models — the  arms  straight 
until  the  body  has  fallen  back  to  an  almost  upright 
position;  then  comes  the  sharp  drop  back  of  the 
shoulders  beyond  the  perpendicular,  the  arms  simul- 
taneously doing  their  work,  so  that  as  the  swing  back 
is  finished,  the  backs  of  the  hands  just  touch  the  ribs 
in  feathering.  All  these  things  are  quite  in  accord- 
ance with  what  used  to  be  considered  the  perfection 
of  rowing.;  and,  indeed,  this  style  of  rowing  has  some 
important  good  qualities  and  a  very  handsome  appear- 
ance. The  lightning  feather,  also,  which  follows  the 
long  sweeping  stroke,  is  theoretically  perfect.  Now, 
in  the  case  of  the  Oxford  crew,  we  observe  a  style 
which  at  first  sight  seems  less  excellent.  As  soon  as 
the  oars  are  dashed  down  and  catch  their  first  hold  of 
the  water,  the  arms  as  well  as  the  shoulders  of  each 
oarsman  are  at  work.*  The  result  is,  that  when  the 

*  I  write  this  with  full  knowledge  that  many  Oxford  men  deny  the 
fact.  I  have  rowed  behind  Cambrid'ge,  Oxford,  and  London  strokes,  and 
hare  several  times  taken  the  place  (number  2  thwart)  of  a  London  water- 
man in  a  four  ("  stroke  "  by  John  Mackinney)  training  for  the  Thames 
Regatta.  So  that  I  have  had  ample  opportunities  for  comparing  different 
rowing  styles ;  and  I  am  satisfied  that  the  main  defect  of  the  real  Cam- 
bridge style  was  (and  perhaps  is)  an  exaggeration  of  the  sound  rule  that 
a  boat  should  be  propelled  rather  by  the  body  than  by  the  arms.  The 
very  swing  hi  a  Cambridge  boat  shows  that  this  must  be  so.  On  the 
other  hand,  the  Thames  watermen  do  too  much  arm-work ;  and  hence 
seem  to  double  a  little  over  their  oars.  I  once  rowed  with  some  Cam- 
bridge friends  from  London  nearly  to  Oxford  and  back,  taking  a  Thames 
waterman  as  "  help."  We  set  him,  at  first,  for  our  strokesman,  but  pres- 
ently made  him  row  bow,  for  we  could  none  of  us  stand  his  gripping, 
arm-working  style. 


298  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

back  lias  readied  an  upright  position,  the  arms  have 
already  reached  the  chest,  and  the  stroke  is  finished. 
Thus  the  Oxford  stroke  takes  a  perceptibly  shorter 
time  than  the  Cambridge  stroke ;  it  is  also,  necessarily, 
somewhat  shorter  in  the  water.  One  would,  therefore, 
say  it  must  be  less  effective.  Especially  would  an 
unpractised  observer  form  this  opinion,  because  the 
Oxford  stroke  seems  to  be  much  shorter  in.  range  than 
it  is  in  reality.  There  we  have  the  secret  of  its 
efficiency.  It  is  actually  nearly  as  long  as  ;the  Cam- 
bridge stroke,  but  is  taken  in  a  perceptibly  shorter 
time.  What  does  this  mean  but  that  the  oar  is  taken 
much  more  sharply,  and,  therefore,  much  more  effec- 
tively, through  the  water  ? 

Much  more  effectively  so  far  as  the  actual  condi- 
tions of  the  contest  are  concerned.  The  modern 
racing  outrigger  requires  a  sharp  impulse,  because  it 
will  take  almost  any  speed  we  can  apply  to  it.  It 
will  also  retain  that  speed  between  the  strokes,  a  con- 
sideration of  great  importance.  The  old-fashioned 
racing-eights  required  to  be  continually  under  propul- 
sion. The  lightning-feather  was  a  necessity  in  their 
case,  for  between  every  stroke  the  boat  would  lag  ter- 
ribly with  a  slow-feathering  crew.  "We  do  not  say,  of 
course,  that  the  speed  of  a  light  outrigged  craft  does 
not  diminish  between  the  strokes.  Any  one  who  has 
watched  a  closely-contested  bumping-race,  and  noticed 
the  way  in  which  the  sharply-cut  bow  of  the  pursuing 


OXFORD  AND   CAMBRIDGE  ROWING  STYLES.          299 

boat  draws  up  to  the  rudder  of  the  other  as  by  a  suc- 
cession of  impulses,  although  either  boat  seen  alone 
would  seem  to  sweep  on  with  almost  uniform  speed, 
will  know  that  the  motion  of  the  lightest  boat  is  not 
strictly  uniform.  But  there  is  an  immense  difference 
between  the  almost  imperceptible  loss  of  way  of  a 
modern  eight  and  the  dead  "lag"  in  the  old-fashioned 
craft.  And  hence  we  get  the  following  important  con- 
sideration :  Whereas  with  the  old  boats  it  was  useless 
for  a  crew  to  attempt  to  give  a  very  quick  motion 
to  their  boat  by  a  sharp,  sudden  "lift,"  this  plan  is 
calculated  to  be,  of  all  others,  the  most  effective  with 
the  modern  racing-eight. 

It  may  seem,  at  first  sight,  that,  after  all,  the  result 
of  the  Cambridge  style  should  be  as  effective  as  that 
of  the  other.  If  arms  and  shoulders  do  their  work 
in  both,  crews  with  equal  energy — which  we  may 
assume  to  be  the  case— and  if  the  number  of  strokes 
per  minute  is  equal,  the  actual  propulsive  energy 
ought  to  be  equal  likewise.  A  little  consideration 
will  show  that  this  is  a  fallacy.  If  two  men  pull  at 
a  weight  together  they  will  move  it  farther  with  a 
given  expenditure  of  energy  than  if  first  one  and 
then  the  other  apply  his  strength  to  the  work.  And, 
what  is  more  to  the  purpose,  they  will  be  able  to 
move  it  faster.  So  shoulders  and  arms  working  simul- 
taneously will  give  a  greater  propulsive  power  than 
when  working  separately,  even  though  in  the  latter 


300  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

case  each  works  with  its  fullest  energy.  And  not 
only  so,  but  by  the  simultaneous  use  of  arms  and 
shoulders,  that  sharpness  of  motion  can  alone  be  given 
which  is  essential  to  the  propulsion  of  a  modern  racing- 
boat. 

We  have  said  that  the  two  crews  are  severally 
rowing  in  the  style  which  has  lately  been  peculiar  to 
their  respective  universities.  But  the  Cambridge  crew 
is  rowing  in  that  form  of  the  Cambridge  style  which 
brings  it  nearest  to  the  requirements  of  modern  racing. 
The  faults  of  the  style  are  subdued,  so  to  speak,  and 
its  best  qualities  brought  out  effectually.  In  one  or 
two  of  the  long  series  of  defeats  lately  sustained  by 
Cambridge  the  reverse  has  been  the  case.  At  present, 
too,  there  is  a  certain  roughness  about  the  Oxford  crew 
which  encourages  the  hopes  of  the  light-blue  supporters. 
But  it  must  be  admitted  that  this  roughness  is  rather 
apparent  than  real,  great  as  it  seems,  and  it  will 
doubtless  disappear  before  the  day  of  encounter. 
We  venture  to  predict  that  the  "time"  of  the  ap- 
proaching race,  taken  in  conjunction  with  the  state  of 
the  tide,  will  show  the  present  crews  to  be  at  least 
equal  to  the  average.* 

*  The  race  (that  of  1869)  was  one  of  the  best  ever  rowed,  and  the 
time  of  the  winners  (Oxford)  better  than  in  any  former  race. 

(From  the  Daily  News,  April,  1869.) 


THE  STATE   OF  THE  ODDS.  3Q1 


BETTING  ON  HORSE-RACES:   OR,  THE  STATE 
OF   THE   ODDS. 

THERE  appears  every  day  in  the  newspapers  an 
account  of  the  betting  on  the  principal  forthcoming 
races.  The  betting  on  such  races  as  the  Two  Thou- 
sand Guineas,  the  Derby,  and  the  Oaks,  often  begins 
more  than  a  year  before  the  races  are  run ;  and  during 
the  interval,  the  odds  laid  against  the  different  horses 
engaged  in  them  vary  repeatedly,  in  accordance  with 
the  reported  progress  of  the  animals  in  their  training, 
or  with  what  is  learned  respecting  the  intentions  of 
their  owners.  Many  who  do  not  bet  themselves,  find 
an  interest  in  watching  the  varying  fortunes  of  the 
horses,  which  are  held  by  the  initiated  to  be  leading 
favorites,  or  to  fall  into  the  second  rank,  or  merely  to 
have  an  outside  chance  of  success.  It  is  amusing  to 
notice,  too,  how  frequently  the  final  state  of  the  odds 
is  falsified  by  the  event ;  how  some  "  rank  outsider " 
will  run  into  the  first  place,  while  the  leading  favorites 
are  not  even  "  placed." 

It  is  in  reality  a  simple  matter  to  understand 
the  betting  on  races  (or  contests  of  any  kind),  yet 
it  is  astonishing  how  seldom  those  who  do  not  ac- 
tually bet  upon  races  have  any  inkling  of  the  mean- 
ing of  those  mysterious  columns  which  indicate  the 
opinion  of  the  betting  world  respecting  the  proba- 


302  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

ble  results  of  approaching  contests,  equine  or  other- 
wise. 

Let  us  take  a  few  simple  cases  of  u  odds,"  to  begin 
with  5  and,  having  mastered  the  elements  of  our  sub- 
ject, proceed  to  see  how  cases  of  greater  complexity 
are  to  be  dealt  with. 

Suppose  the  newspapers  inform  us  that  the  betting 
is  2  to  1  against  a  certain  horse  for  such  and  such  a 
race,  what  inference  are  we  to  deduce  ?  To  learn  this, 
let  us  conceive  a  case  in  which  the  true  odds  against  a 
certain  event  are  as  2  to  1.  Suppose  there  are  three 
balls  in  a  bag,  one  being  white,  the  others  black. 
Then,. if  we  draw  a  ball  at  random,  it  is  clear  that  we 
are  twice  as  likely  to  draw  a  black  as  to  draw  a  white 
ball.  This  is  technically  expressed  by  saying  that  the 
odds  are  2  to  1  against  drawing  a  white  ball ;  or  2  to  1 
on  (that,  is  in  favor  of)  drawing  a  black  ball.  This 
being  understood,  it  follows  that,  when  the  odds  are 
said  to  be  2  to  1  against  a  certain  horse,  we  are  to  infer 
that,  in  the  opinion  of  those  who  have  studied  the 
performance  of  the  horse,  and  compared  it  with  that 
of  the  other  horses  engaged  in  the  race,  his  chance  of 
winning  is  equivalent  to  the  chance  of  drawing  one 
particular  ball  out  of  a  bag  of  three  balls. 

Observe  how  this  result  is  obtained :  the  odds  are  2 
to  1,  and  the  chance  of  the  horse  is  as  that  of  drawing 
one  ball  out  of  a  bag  of  three — three  being  the  sum  of 
the  two  numbers  2  and  1.  This  is  the  method  followed 


THE  STATE  OF  THE  ODDS.  303 

in  all  such  cases.  Tims,  if  tlie  odds  against  a  horse 
are  7"  to  1,  we  infer  that  the  cognoscenti  consider  his 
chance  equal  to  that  of  drawing  one  particular  ball 
out  of  a  bag  of  eight. 

A  similar  treatment  applies  when  the  odds  are  not 
given  as  so  many  to  one.  Thus,  if  the  odds  against  a 
horse  are  as  5  to  2,  we  infer  that  the  horse's  chance  is 
equal  to  that  of  drawing  a  white  ball  out  of  a  bag 
containing  five  black  and  two  white  balls — or  seven 
in  all. 

We  must  notice  also  that  the  number  of  balls  may 
be  increased  to  any  extent,  provided  the  proportion 
between  the  total  number  and  the  number  of  a  specified 
color  remains  unchanged.  Thus,  if  the  odds  are  5  to 
1  against  a  horse,  his  chance  is  assumed  to  be  equiva- 
lent to  that  of  drawing  one  white  ball  out  of  a  bag 
containing  six  balls,  only  one  of  which  is  white ;  or  to 
that  of  drawing  a  white  ball  out  of  a  bag  containing 
sixty  balls,  of  which  ten  are  white — and  so  on.  This 
is  a  very  important  principle,  as  we  shall  now  see. 

Suppose  there  are  two  horses  (among  others)  en- 
gaged in  a  race,  and  that  the  odds  are  2  to  1  against 
one,  and  4  to  1  against  the  other — what  are  the  odds 
that  one  of  the  two  horses  will  win  the  race  ?  This 
case  will  doubtless  remind  our  readers  of  an  amusing 
sketch  by  Leech,  called — if  we  remember  rightly— 
"Signs  of  the  Commission."  Three  or  four  under- 
graduates are  at  a  "wine,"  discussing  matters  equine. 


304  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

One  propounds  to  his  neighbor  the  following  ques- 
tion :  "  I  say,  Charley,  if  the  odds  are  2  to  1  against 
Rataplan,  and  4  to  1  against  Quick  March,  what's 
the  betting  about  the  pair  ? " — "  Don't  know,  I'm  sure," 
replies  Charley;  "but  I'll  give  you  6  to  1  against 
them."  The  absurdity  of  the  reply  is,  of  course,  very 
obvious;  we  see  at  once  that  the  odds  cannot  be 
heavier  against  a  pair  of  horses  than  against  either 
singly.  Still  there  are  many  who  would  not  find  it 
easy  to  give  a  correct  reply  to  the  question.  What 
has  been  said  above,  however,  will  enable  us  at  once 
to  determine  the  just  odds  in  this  or  any  similar  case. 
Thus— -the  odds  against  one  horse  being  2  to  1,  his 
chance  of  winning  is  equal  to  that  of  drawing  one 
white  ball  out  of  a  bag  of  three,  one  only  of  which  is 
white.  In  like  manner,  the  chance  of  the  second  horse 
is  equal  to  that  of  drawing  one  white  ball  out  of  a  bag 
of  five,  one  only  of  which  is  white.  Now  we  have  to 
find  a  number  wrhich  is  a  multiple  of  both  the  numbers 
three  and  five.  Fifteen  is  such  a  number.  The  chance 
of  the  first  horse,  modified  according  to  the  principle 
explained  above,  is  equal  to  that  of  drawing  a  white 
ball  out  of  a  bag  of  fifteen  of  which  fne  are  white.  In 
like  manner,  the  chance  of  the  second  is  equal  to  that 
of  drawing  a  white  ball  out  of  a  bag  of  fifteen  of  which 
three  are  white.  Therefore,  the  chance  that  one  of 
the  two  will  win  is  equal  to  that  of  drawing  a  white 
ball  out  of  a  bag  of  fifteen  balls  of  which  eight  (five 


THE  STATE   OF  THE  ODDS.  305 

added  to  three)  are  white.  There  remain  seven  black 
balls,  and  therefore  the  odds  are  8  to  7  on  the  pair. 

To  impress  the  method  of  treating  such  cases  on  the 
mind  of  the  reader,  we  take  the  betting  about  three 
horses — say  3  to  1,  7  to  2,  and  9  to  1,  against  the  three 
horses  respectively.  Then  their  respective  chances 
are  equal  to  the  chance  of  drawing  (1)  one  white  ball 
out  of  four,  one  only  of  which  is  white;  (2)  a  white 
ball  out  of  nine,  of  which  two  only  are  white ;  and  (3) 
one  white  ball  out  of  ten,  one  only  of  which  is  white. 
The  least  number  which  contains  four,  nine,  and  ten, 
is  180;  and  the  above  chances,  modified  according  to 
the  principle  explained  above,  become  equal  to  the 
chance  of  drawing  a  white  ball  out  of  a  bag  containing 
180  balls,  when  45,  40,  and  18  (respectively)  are  white. 
Therefore,  the  chance  that  one  of  the  three  will  win  is 
equal  to  that  of  drawing  a  white  ball  out  of  a  bag  con- 
taining 180  balls,  of  which  103  (the  sum  of  45,  40,  and 
18)  are  white.  Therefore,  the  odds  are  103  to  77  on 
the  three. 

One  does  not  hear  in  practice  of  such  odds  as  103 
to  77.  But  betting-men  (whether  or  not  they  apply 
just  principles  of  computation  to  such  questions,  is 
unknown  to  us)  manage  to  run  very  near  the  truth. 
For  instance,  in  such  a  case  as  the  above,  the  odds  on 
the  three  would  probably  be  given  as  4  to  3 — that  is, 
instead  of  103  to  77,  or,  which  is  the  same  thing.  412 
to  308,  the  published  odds  would  be  412  to  309. 


306  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

And  here  a  certain  nicety  in  betting  has  to  be  men- 
tioned. In  running  the  eye  down  the  list  of  odds,  one 
will  often  meet  such  expressions  as  10  to  1  against 
such  a  horse  offered,  or  10  to  1  wanted.  Now,  the 
odds  of  10  to  1  taken  may  be  understood  to  imply  that 
the  horse's  chance  is  equivalent  to  that  of  drawing  a 
certain  ball  out  of  a  bag  of  eleven.  But  if  the  odds 
are  offered  and  not  taken,  we  cannot  infer  this.  The 
offering  of  the  odds  implies  that  the  horse's  chance  is 
not  letter  than  that  above  mentioned,  but  the  fact  that 
they  are  not  taken  implies  that  the  horse's  chance  is 
not  so  good.  If  no  higher  odds  are  offered  against  the 
horse,  we  may  infer  that  his  chance  is  very  little  worse 
than  that  mentioned  above.  Similarly,  if  the  odds  of 
10  to  1  are  asked  for,  we  infer  that  the  horse's  chance 
is  not  worse  than  that  of  drawing  one  ball  out  of 
eleven ;  if  the  odds  are  not  obtained,  we  infer  that  his 
chance  is  "better ;  and  if  no  lower  odds  are  asked  for, 
we  infer  that  his  chance  is  very  little  letter. 

Thus,  there  might  be  three  horses  (A,  B,  and  C) 
against  whom  the  nominal  odds  were  10  to  1,  and  yet 
these  horses  might  not  be  equally  good  favorites,  be- 
cause the  odds  might  not  be  taken,  or  might  be  asked 
for  in  vain.  We  might  accordingly  find  three  such 
horses  arranged  thus : 

Odds. 

A        .        .        .        10  to  1  (wanted). 

13        .        .        .         10  to  1  (taken). 

0        .        .        .        10  to  1  (offered). 


THE  STATE   OF  THE  ODDS.  307 

Or  these  different  stages  might  mark  the  upward  or 
downward  progress  of  the  same  horse  in  the  betting. 
In  fact,  there  are  yet  more  delicate  gradations, 
marked  by  such  expressions  respecting  certain  odds,  as 
— offered  freely,  offered,  offered  and  taken  (meaning 
that  some  offers  only  have  been  accepted),  taken,  taken 
and  wanted,  wanted,  and  so  on. 

As  an  illustration  of  some  of  the  principles  we 
have  been  considering,  let  us  take  from  the  day's 
paper  *  the  state  of  the  odds  respecting  the  "  Two 
Thousand  Guineas."  It  is  presented  in  the  following 
form : 

TWO   THOUSAND   GUINEAS. 

7  to  2  against  Rosicrucian  (off.). 
6  to  1  against  Pace  (off. ;  V  to  1  w.). 
10  to  1  against  Green  Sleeve  (off.). 
100  to  7"  against  Blue  Gown  (off.). 
180  to  80  against  Sir  J.  Hawley's  lot  (t.). 

This  table  is  interpreted  thus  :  bettors  are  willing  to 
lay  the  same  odds  against  Hosierucian  as  would  be  the 
true  mathematical  odds  against  drawing  a  white  ball 
out  of  a  bag  containing  two  white  and  seven  black 
balls ;  but  no  one  is  willing  to  back  the  horse  at  this 
rate.  On  the  other  hand,  higher  odds  are  not  offered 
against  him.  Hence  it  is  presumable  that  his  chance 
is  somewhat  less  than  that  above  indicated.  Again, 
bettors  are  willing  to  lay  the  same  odds  against  Pace 
as  might  fairly  be  laid  against  drawing  one  white  ball 

*  This  article  was  written  early  in  March,  1868. 


308  LIGHT   SCIENCE  FOR  LEISURE  HOURS. 

out  of  a  bag  of  seven,  one  only  of  which  is  white ;  but 
backers  of  the  horse  consider  that  they  ought  to  get 
the  same  odds  as  might  be  fairly  laid  against  drawing 
the  white  ball  when  an  additional  black  ball  had  been 
put  into  the  bag.  As  respects  Green  Sleeve  and  Blue 
Gown,  bettors  are  willing  to  lay  the  odds  which  there 
would  be,  respectively,  against  drawing  a  white  ball 
out  of  a  bag  containing — (1)  eleven  balls,  one  only  of 
which  is  white,  and  (2)  one  hundred  and  seven  balls, 
seven  only  of  which  are  white.  Now,  the  three  horses 
Rosicrucian,  Green  Sleeve,  and  Blue  Gown,  all  belong 
to  Sir  Joseph  Hawley,  so  that  the  odds  about  the 
three  are  referred  to  in  the  last  statement  of  the  list 
just  given.  And  since  none  of  the  offers  against  the 
three  horses  have  been  taken,  we  may  expect  the  odds 
actually  taken  about  "  Sir  Joseph  Hawley's  lot "  to  be 
more  favorable  than  those  obtained  by  summing  up 
the  three  former  in  the  manner  we  have  already 
examined.  It  will  be  found  that  the  resulting  odds 
(offered)  against  Sir  J.  Hawley's  lot — estimated  in  this 
way — should  be,  as  nearly  as  possible,  132  to  80.  We 
find,  however,  that  the  odds  taken  are  180  to  80. 
Hence,  we  learn  that  the  offers  against  some  or  all  of 
the  three  horses  are  considerably  short  of  what  back- 
ers require ;  or  else,  that  some  person  has  been  induced 
to  offer  far  heavier  odds  against  Sir  J.  Hawley's  lot 
than  are  justified  by  the  fair  odds  against  his  horses, 
severally. 


THE  STATE  OF  THE  ODDS.  309 

We  have  lieard  it  asked  why  a  horse  is  said  to  be  a 
favorite,  though  the  odds  may  be  against  him.  This 
is  very  easily  explained.  Let  us  take  as  an  illustration 
the  case  of  a  race  in  which  four  horses  are  engaged  to 
run.  If  all  these  horses  had  an  equal  chance  of  win- 
ning, it  is  very  clear  that  the  case  would  correspond  to 
that  of  a  bag  containing  four  balls  of  different  colors ; 
since,  in  this  case,  we  should  have  an  equal  chance  of 
drawing  a  ball  of  any  assigned  color.  Now,  the  odds 
against  drawing  a  particular  ball  would  clearly  be  3  to 
1.  This,  then,  should  be  the  betting  against  each  of 
the  three  horses.  If  any  one  of  the  horses  has  less 
odds  offered  against  him,  he  is  afcworite.  There  may 
be  more  than  one  of  the  four  horses  thus  distinguished ; 
and  in  that  case,  the  horse  against  which  the  least  odds 
are  offered  is  the  first  favorite.  Let  us  suppose  there 
are  two  favorites,  and  that  the  odds  against  the  lead- 
ing favorite  are  3  to  2,  those  against  the  other  2  to  1, 
and  those  against  the  best  non-favorite  4  to  1 ;  and 
let  us  compare  the  chance  of  the  four  horses.  We 
have  not  named  any  odds  against  the  fourth,  because, 
if  the  odds  against  all  the  horses  but  one  are  given,  the 
just  odds  against  that  one  are  determinable,  as  we  shall 
Bee  immediately.  The  chance  of  the  leading  favorite 
corresponds  to  the  chance  of  drawing  a  ball  out  of  a 
bag  in  which  are  three  black  and  two  white  balls,  five 
in  all ;  that  of  the  next  to  the  chance  of  drawing  a  ball 
out  of  a  bag  in  which  are  two  black  and  one  white  ball, 


310  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

three  in  all ;  that  of  the  third,  to  the  chance  of  drawing 
a  ball  out  of  a  bag  in  which  are  four  black  balls  and 
one  white  one,  Jive  in  all.  We  take,  then,  the  least 
number  containing  both  five  and  three — that  is,  fif- 
teen; and  then  the  number  of  white  balls,  correspond- 
ing to  the  chances  of  the  three  horses,  are  respectively 
six,  five,  and  three,  or  fourteen  in  all ;  leaving  only  one 
to  represent  the  chance  of  the  fourth  horse  (against 
which  the  odds  are,  therefore,  14  to  1).  Hence  the 
chances  of  the  four  horses  are  respectively  as  the  num- 
bers six,,  five,  three,  and  one. 

We  have  spoken  above  of  the  published  odds.  The 
statements  made  in  the  daily  papers  commonly  refer 
to  wagers  actually  made,  and  therefore  the  uninitiated 
might  suppose  that  every  one  who  tried  would  be  able 
to  obtain  the  same  odds.  This  is  not  the  case.  The 
wagers  which  are  laid  between  practised  betting-men 
afford  very  little  indication  of  the  prices  which  would 
be  forced  (so  to  speak)  upon  an  inexperienced  bettor. 
Book-makers — that  is,  men  who  make  a  series  of  bets 
upon  several  or  all  of  the  horses  engaged  in  a  race — 
naturally  seek  to  give  less  favorable  terms  than  the 
known  chances  of  the  different  horses  engaged  would 
suffice  to  warrant.  As  they  cannot  offer  such  terms  to 
the  initiated,  they  offer  them — and  in  general  success- 
fully— to  the  inexperienced. 

It  is  often  said  that  a  man  may  so  lay  his  wagers 
about  a  race  as  to  make  sure  of  gaining  money  which- 


THE  STATE  OF  THE  ODDS.  311 

ever  horse  wins  the  race.  This  is  not  strictly  the  case. 
It  is  of  course  possible  to  make  sure  of  winning  if  the 
bettor  can  only  get  persons  to  lay  or  take  the  odds  he 
requires  to  the  amount  he  requires.  But  this  is  pre- 
cisely the  problem  which  would  remain  insoluble  if  all 
bettors  were  equally  experienced. 

Suppose,  for  instance,  that  there  are  three  horses 
engaged  in  a  race  with  equal  chances  of  success.  It  is 
readily  shown  that  the  odds  are  2  to  1  against  each. 
But  if  a  bettor  can  get  a  person  to  take  even  betting 
against  the  first  horse  (A),  a  second  person  to  do  the 
like  about  the  second  horse  (B),  and  a  third  to  do  the 
like  about  the  third  horse  (C),  and  if  all  these  bets 
are  made  to  the  same  amount — say,  £1,000 — then,  in- 
asmuch as  only  one  horse  can  win,  the  bettor  loses 
£1,000  on  that  horse  (say  A),  and  gains  the  same  sum 
on  each  of  the  two  horses  B  and  C.  Thus,  on  the 
whole,  he  gains  £1,000,  the  sum  laid  out  against  eacli 
horse. 

If  the  layer  of  the  odds  had  *aid  the  true  odds  to 
the  same  amount  on  each  horse,  he  would  neither  have 
gained  nor  lost.  Suppose,  for  instance,  that  he  laid 
£1,000  to  £500  against  each  horse,  and  A  won ;  then 
he  would  have  to  pay  £1,000  to  the  backer  of  A,  and 
to  receive  £500  from  each  of  the  backers  of  B  and  C. 
In  like  manner,  a  person  who  had  backed  each  horse 
to  the  same  extent  would  neither  lose  nor  gain  by  the 
event.  Nor  would  a  backer  or  layer  who  had  wagered 


312  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

different  sums  necessarily  gain  or  lose  by  the  race ;  he 
would  gain  or  lose  according  to  the  event.  This  will  at 
once  be  seen,  on  trial : 

Let  us  next  take  the  case  of  horses  with  unequal 
prospects  of  success — for  instance,  take  the  case  of  the 
four  horses  considered  above,  against  which  the  odds 
were  respectively  3  to  2,  2  to  1,  4  to  1,  and  14  to  1. 
Here,  suppose  the  same  sum  laid  against  each,  and  for 
convenience  let  this  sum  be  £84  (because  84  contains 
the  numbers  3,  2,  4,  and  14).  The  layer  of  the  odds 
wagers  £84  to  £56  against  the  leading  favorite,  £84 
to  £42  against  the  second  horse,  £84  to  £21  against  the 
third,  and  £84  to  £6  against  the  fourth.  Whichever 
horse  wins,  the  layer  has  to  pay  £84;  but  if  the 
favorite  wins,  he  receives  only  £42  on  one  horse,  £21 
on  another,  and  £6  on  the  third — that  is  £69  in  all,  so 
that  he  loses  £15  ;  if  the  second  horse  wins,  he  has  to 
receive  £56,  £21,  and  £6 — or  £83  in  all,  so  that  he 
loses  £1 ;  if  the  third  horse  wins,  he  receives  £56,  £42, 
and  £6 — or  £104  in  all,  and  thus  gains  £20 ;  and,  lastly, 
if  the  fourth  horse  wins,  he  has  to  receive  £56,  £42, 
and  £21 — or  119  in  all,  so  that  he  gains  £35.  He 
clearly  risks  much  less  than  he  has  a  chance  (however 
small)  of  gaining.  It  is  also  clear  that  in  all  such  cases 
the  worst  event  for  the  layer  of  the  odds  is,  that  the 
favorite  should  win.  Accordingly,  as  professional 
book-makers  are  nearly  always  layers  of  odds,  one 
often  finds  the  success  of  a  favorite  spoken  of  in  the 


THE  STATE   OF  THE   ODDS.  313 

papers  as  a  "  great  blow  for  the  book-makers,"  while 
the  success  of  a  rank  outsider  will  be  described  as  "  a 
misfortune  to  backers." 

But  there  is  another  circumstance  which  tends  to 
make  the  success  of  a  favorite  a  blow  to  layers  of  the 
odds,  .and  vice  versa.  In  the  case  we  have  supposed, 
the  money  actually  pending  about  the  four  horses 
(that  is,  the  sum  of  the  amounts  laid  for  and  against 
them)  was  £140  as  respects  the  favorite,  £126  as 
respects  the  second,  £105  as  respects  the  third,  and 
£90  as  respects  the  fourth.  But,  as  a  matter  of  fact, 
the  amounts  pending  about  the  favorites  bear  always 
a  much  greater  proportion  than  the  above  to  the 
amounts  pending  about  outsiders.  It  is  easy  to  see 
the  effect  of  this.  Suppose,  for  instance,  that  instead 
of  the  sums  £84  to  £56,  £84  to  £42,  £84  to  £21,  and 
£84  to  £6,  a  book-maker  had  laid  £8,400  to  £5,600, 
£840  to  £420,  £84  to  £21,  and  £14  to  £1,  respective- 
ly— then  it  will  easily  be  seen  that  he  would  lose 
£7,958  by  the  success  of  the  favorite ;  whereas  he  would 
gain  £4,782  by  the  success  of  the  second  horse,  £5,937 
by  that  of  the  third,  and  £6,027  by  that  of  the  fourth. 
We  have  taken  this  as  an  extreme  case ;  as  a  general 
rule,  there  is  not  so  great  a  disparity  as  has  been  here 
assumed  between  the  sums  pending  on  favorites  and 
outsiders. 

Finally,  it  may  be  asked  whether,  in  the  case  of 
horses  having  unequal  chances,  it  is  possible  that 

14 


314  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

wagers  can  be  so  proportioned  (just  odds  being  given 
and  talcen)  that,  as  in  the  former  case,  a  person  back- 
ing, or  laying  against,  all  the  four  shall  neither  gain 
nor  lose.  It  is  so.  All  that  is  necessary  is,  that  the 
sum  actually  pending  about  each  horse  shall  be  the 
same.  Thus,  in  the  preceding  case,  if  the  wagers  £9 
to  £6,  £10  to  £5,  £12  to  £3,  and  £14  to  £1,  are  either 
laid  or  taken  by  the  same  person,  he  will  neither  gain 
nor  lose  by  the  event,  whatever  it  may  be.  And,  there- 
fore, if  unfair  odds  are  laid  or  taken  about  all  the 
horses,  in  such  a  manner  that  the  amounts  pending  on 
the  several  horses  are  equal  (or  nearly  so),  the  unfair 
bettor  must  win  by  the  result.  Say,  for  instance,  that 
instead  of  the  above  odds,  he  lays  £8  to  £6,  £9  to  £5, 
£11  to  £3,  and  £13  to  £1  against  the  four  horses  re- 
spectively ;  it  will  be  found  that  he  must  win  £1.  Or 
if  he  takes  the  odds  £18  to  £11,  £20  to  £9,  £24  to  £5, 
and  £28  to  £1  (the  just  odds  being  £18  to  £12,  £20  to 
£10,  £24  to  £6,  £28  to  £2  respectively),  he  will  win 
£1  by  the  race.  So  that,  by  giving  or  taking  such 
odds  to  a  sufficiently  great  amount,  a  bettor  would  be 
certain  of  pocketing  a  large  sum,  whatever  the  event 
of  a  given  race  might  be. 

In  every  instance,  a  man  who  bets  on  a  race  must 
risk  his  money ,  unless  he  can  succeed  in  taking  un- 
fair advantages  over  those  with  whom  he  bets.  Our 
readers  will  conceive  how  small  must  be  the  chance 
that  an  unpractised  bettor  will  gain  any  thing  but 


SQUARING  TUE   CIRCLE.  315 

dearly-bought  experience  by  speculating  on  horse- 
races. We  would  recommend  those  who  are  tempted 
to  hold  another  opinion  to  follow  the  plan  suggested 
by  Thackeray  in  a  similar  case — to  take  a  good  look 
at  professional  and  practised  betting-men,  and  to  de- 
cide "  which  of  those  men  they  are  most  likely  to  get 
the  better  of"  in  turf  transactions. 

(From  Chambers' s  Journal,  July,  1869.) 


SQUARING   THE   CIRCLE. 

THERE  must  be  a  singular  charm  about  insoluble 
problems,  since  there  are  never  wanting  persons  who 
are  willing  to  attack  them.  We  doubt  not  that  at 
this  moment  there  are  persons  who  are  devoting  their 
energies  to  Squaring  the  Circle,  in  the  full  belief 
that  important  advantages  would  accrue  to  science — 
and  possibly  a  considerable  pecuniary  profit  to  them- 
selves— if  they  could  succeed  in  solving  it.  Quite 
recently,  applications  have  been  made  to  the  Paris 
Academy  of  Sciences,  to  ascertain  what  was  the 
amount  which  that  body  was  authorized  to  pay  over 
to  any  one  who  should  square  the  circle.  So  seri- 
ously, indeed,  was  the  secretary  annoyed  by  appli- 
cations of  this  sort,  that  it  was  found  necessary  to 
announce  in  the  daily  journals  that  not  only  was  the 
Academy  not  authorized  to  pay  any  sum  at  all,  but 


316  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

that  it  had  determined  never  to  give  the  least  at- 
tention to  those  who  fancied  they  had  mastered  the 
famous  problem. 

It  is  a  singular  circumstance  that  people  have  even 
attacked  the  problem  without  knowing  exactly  what 
its  nature  is.  One  ingenious  workman,  to  whom  the 
difficulty  had  been  propounded,  actually  set  to  work 
to  invent  an  arrangement  for  measuring  the  circum- 
ference of  the  circle ;  and  was  perfectly  satisfied  that 
he  had  thus  solved  a  problem  which  had  mastered  all 
the  mathematicians  of  ancient  and  modern  times. 
That  we  may  not  fall  into  a  similar  error,  let  us  clearly 
understand  what  it  is  that  is  required  for  the  solution 
of  the  problem  of  "  squaring  the  circle." 

To  begin  with,  we  must  note  that  the  term  "  squar- 
ing the  circle "  is  rather  a  misnomer  ;  because  the 
true  problem  to  be  solved  is  the  determination  of  the 
length  of  a  circle's  circumference  when  the  diameter 
is  known.  Of  course,  the  solution  of  this  problem, 
or,  as  it  is  termed,  the  rectification  of  the  circle,  in- 
volves the  solution  of  the  other,  or  the  quadrature  of 
the  circle.  But  it  is  well  to  keep  the  simpler  issue 
before  us. 

Many  have  supposed  that  there  exists  some  exact 
relation  between  the  circumference  and  the  diameter 
of  the  circle,  and  that  the  problem  to  be  solved  is  the 
determination  of  this  relation.  Suppose,  for  example, 
that  the  approximate  relation  discovered  by  Archi- 


SQUARING  THE   CIRCLE.  317 

medes  (who  found,  that  if  a  circle's  diameter  is  repre- 
sented by  seven,  the  circumference  may  be  almost 
exactly  represented  by  twenty-two)  were  strictly  cor- 
rect, and  that  Archimedes  had  proved  it  to  be  so : 
then,  according  to  this  view,  he  would  have  solved  the 
great  problem ;  and  it  is  to  determine  a  relation  of 
some  such  sort  that  many  persons  have  set  themselves. 
Now,  undoubtedly,  if  any  relation  of  this  sort  could  be 
established,  the  problem  would  be  solved ;  but,  as  a 
matter  of  fact,  no  such  relation  exists,  and  the  solu- 
tion of  the  problem  does  not  require  that  there  should 
be  any  relation  of  the  sort.  For  example,  we  do  not 
look  on  the  determination  of  the  diagonal  of  a  square 
(whose  side  is  known)  as  an  insoluble,  or  as  otherwise 
than  a  very  simple  problem.  Yet  in  this  case  no 
exact  relation  exists.  We  cannot  possibly  express 
both  the  side  and  the  diagonal  of  a  square  in  whole 
numbers,  no  matter  what  unit  of  measurement  we 
adopt :  or,  to  put  the  matter  in  another  way,  we  can- 
not possibly  divide  both  the  side  and  the  diagonal 
into  equal  parts  (which  shall  be  the  same  along  each), 
no  matter  how  small  we  take  the  parts.  If  we  divide 
the  side  into  1,000  parts,  there  will  be  1,414  such 
parts,  and  a  piece  over,  in  the  diagonal ;  if  we  divide 
the  side  into  10,000  parts,  there  will  be  14,142,  and 
still  a  little  piece  over,  in  the  diagonal ;  and  so  on  for 
ever.  Similarly,  the  mere  fact  that  no  exact  relation 
exists  between  the  diameter  and  the  circumference  of 


318  LIGHT   SCIENCE   FOR  LEISURE  HOURS. 

a  circle  is  no  bar  whatever  to  the  solution  of  the  great 
problem. 

Before  leaving  this  part  of  the  subject,  however, 
we  may  mention  a  relation  which  is  very  easily  re- 
membered, and  is  very  nearly  exact — much  more  so, 
at  any  rate,  than  that  of  Archimedes.  "Write  down 
the  numbers  113355,  that  is,  the  first  three  odd  num- 
bers each  repeated  twice  over.  Then  separate  the 
six  numbers  into  two  sets  of  three,  thus  :  113)355, 
and  proceed  with  the  division  thus  indicated.  The 
result,  3.1415929  .  .  .  .  ,  expresses  the  circumference 
of  a  circle  whose  diameter  is  1,  correctly  to  the  sixth 
decimal  place,  the  true  relation  being  3.14159265  .... 

Again,  many  people  imagine  that  mathematicians 
are  still  in  a  state  of  uncertainty  as  to  the  relation 
which  exists  between  the  circumference  and  the  diam- 
eter of  the  circle.  If  this  were  so,  scientific  societies 
might  well  hold  out  a  reward  to  any  one  who  could 
enlighten  them  ;  for  the  determination  of  this  relation 
(with  satisfactory  exactitude)  may  be  held  to  lie  at  the 
foundation  of  the  whole  of  our  modern  system  of 
mathematics.  We  need  hardly  say  that  no  doubt 
whatever  rests  on  the  matter.  A  hundred  different 
methods  are  known  to  mathematicians  by  which  the 
circumference  may  be  calculated  from  the  diameter 
with  any  required  degree  of  exactness.  Here  is  a 
simple  one,  for  example:  Take  any  number  of  the 
fractions  formed  by  putting  one  as  a  numerator  over 


SQUARING  THE   CIRCLE.  319 

the  successive  odd  numbers.  Add  together  the  alter- 
nate ones  beginning  with  the  first,  which,  of  course, 
is  unity.  Add  together  the  remainder.  Subtract  the 
second  sum  from  the  first.  The  remainder  will  express 
the  circumference  (the  diameter  being  taken  as  unity) 
to  any  required  degree  of  exactness.  "We  have  merely 
to  take  enough  fractions.  The  process  would,  of 
course,  be  a  very  laborious  one,  if  great  exactness  were 
required,  and  as  a  matter  of  fact,  mathematicians  have 
made  use  of  much  more  convenient  methods  for  de- 
termining the  required  relation ;  but  the  method  is 
strictly  exact. 

The  largest  circle  we  have  much  to  do  with  in 
scientific  questions  is  the  earth's  equator.  As  a  matter 
of.  curiosity,  we  may  inquire  what  the  circumference 
of  the  earth's  orbit  is ;  but  as  we  are  far  from  being 
sure  of  the  exact  length  of  the  radius  of  that  orbit 
(that  is,  of  the  earth's  distance  from  the  sun),  it  is 
clear  that  we  do  not  need  a  very  exact  relation 
between  the  circumference  and  the  diameter  in  deal- 
ing with  that  enormous  circle.  Confining  ourselves, 
therefore,  to  the  circle  of  the  earth's  equator,  let  us 
see  what  exactness  we  seem  to  require.  We  will 
suppose  for  a  moment  that  it  is  possible  to  measure 
round  the  earth's  equator  without  losing  count  of  a 
single  yard,  and  that  we  want  to  gather  from  our 
estimate  what  the  diameter  of  this  great  circle  may 
be.  This  seems,  indeed,  the  only  .use  to  which,  in 


320  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

this  case,  we  can  put  our  knowledge  of  the  relation 
we  are  dealing  with.  We  have  then  a  circle  some 
twenty-five  thousand  miles  round,  and  each  mile  con- 
tains one  thousand  seven  hundred  and  sixty  yards; 
or,  in  all,  there  are  some  forty-four  million  yards  in  the 
circumference,  and  therefore  (roughly)  some  fourteen 
million  yards  in  the  diameter  of  this  great  circle. 
Hence,  if  our  relation  is  correct  within  a  fourteen- 
millionth  part  of  the  diameter,  or  forty-four-millionth 
part  of  the  circumference,  we  are  safe  from  any  error 
exceeding  a  yard.  All  we  want,  then,  is  that  the 
number  expressing  the  circumference  (the  diameter 
being  unity)  should  be  true  to  the  eighth  decimal 
place,  as  quoted  above. 

But,  as  we  have  said,  mathematicians  have  not  been 
content  with  a  computation  of  this  sort.  They  have 
calculated  the  number  not  to  the  eighth,  but  to  the 
six  hundred  and  twentieth  decimal  place.  Now,  if  we 
remember  that  each  new  decimal  makes  the  result  ten 
times  more  exact,  we  shall  begin  to  see  what  a  waste 
of  time  there  has  been  in  this  tremendous  calculation. 
"We  all  remember  the  story  of  the  horse  which  had 
twenty-four  nails  in  its  shoes,  and  was  valued  at  the 
sum  obtained  by  adding  together  a  farthing  for  the 
first  nail,  a  halfpenny  for  the  next,  a  penny  for  the 
next,  and  so  on ;  doubling  twenty-four  times.  The 
result  was  counted  by  thousands  of  pounds.  The 
old  miser  who  paid  at  a  similar  rate  for  a  grave 


SQUARING  THE  CIRCLE.  321 

eighteen  feet  deep  (doubling  for  each  foot),  killed 
himself  when  he  heard  the  total.  But  now  consider 
the  effect  of  multiplying  by  ten,  six  hundred  and 
twenty  times.  A  fraction,  with  that  enormous  number 
for  denominator,  and  unity  for  numerator,  expresses 
the  minuteness  of  the  error  which  would  result  if 
the  "long  value"  of  the  circumference  were  made 
use  of.  Let  an  illustration  present  the  meaning  of 
this  :— 

It  has  been  estimated  that  light,  which  could  eight 
times  circle  the  earth  in  a  second,  takes  50,000  years 
in  reaching  us  from  the  faintest  star  seen  in  Lord 
Rosse's  giant  reflector.  Suppose  we  knew  the  exact 
length  of  the  tremendous  line  which  extends  from  the 
earth  to  such  a  star,  and  wanted,  for  some  incon- 
ceivable purpose,  to  know  the  length  of  the  circum- 
ference of  a  circle  of  which  that  line  was  the  radius. 
The  value  deduced  from  the  above-mentioned  calcula- 
tion of  the  relation  between  the  circumference  and  the 
the  diameter  would  differ  from  the  truth  by  a  length 
which  would  be  imperceptible  under  the  most  powerful 
microscope  ever  yet  constructed.  Nay,  the  radius  we 
have  conceived,  enormous  as  it  is,  might  be  increased 
a  million-fold,  or  a  million  times  a  million-fold,  with 
the  same  result.  And  the  area  of  the  circle  formed 
with  this  increased  radius  would  be  determinate  with 
so  much  accuracy,  that  the  error,  if  presented  in  the 
form  of  a  minute  square,  would  be  utterly  irnpercep- 


.322  LIGHT   SCIENCE  FOR  LEISURE   HOURS. 

tible  under  a  microscope  a  million  times  more  power- 
ful than  the  best  ever  yet  constructed  by  man. 

Not  only  has  the  length  of  the  circumference  been 
calculated  once  in  this  unnecessarily  exact  manner, 
but  a  second  calculator  has  gone  over  the  work  inde- 
pendently. The  two  results  are  of  course  identical 
figure  for  figure. 

It  will  be  asked  then,  what  is  the  problem  about 
which  so  great  a  work  has  been  made  ?  The  problem 
is,  in  fact,  utterly  insignificant;  its  only  interest  lies 
in  the  fact  that  it  is  insoluble — a  property  which  it 
shares  along  with  many  other  problems,  as  the  tri- 
section  of  an  angle,  the  duplication  of  a  cube,  and 
so  on. 

The  problem  is  simply  this :  Having  given  the  dia- 
meter of  a  circle,  to  determine,  "by  a  geometrical  con- 
struction, in  which  only  straight  lines  and  circles  shall 
l)e  made  use  of,  the  side  of  a  square  equal  in  area  to 
the  circle.  As  we  have  said,  the  problem  is  solved, 
if,  by  a  construction  of  the  kind  described,  we  can 
determine  the  length  of  the  circumference ;  because 
then  the  rectangle  under  half  this  length  and  the 
radius  is  equal  in  area  to  the  circle,  and  it  is  a  simple 
problem  to  describe  a  square  equal  to  a  given  rectangle. 

To  illustrate  the  kind  of  construction  required,  we 
give  an  approximate  solution  which  is  remarkably  sim- 
ple, and,  so  far  as  we  are  aware,  not  generally  known. 
Describe  a  square  about  the  given  circle,  touching  it 


SQUARING  THE   CIRCLE.  323 

at  the  ends  of  two  diameters,  AOB,  COD,  at  right 
angles  to  each  other,  and  join  CA ;  let  COAE  be 
one  of  the  quarters  of  the  circumscribing  square,  and 
from  E  draw  EG,  cutting  off  from  AO  a  fourth  part 
AG-  of  its  length,  and  from  AC  the  portion  AH. 
Then  three  sides  of  the  circumscribing  square  together 
with  AH  are  very  nearly  equal  to  the  circumference 
of  the  circle.  The  difference  is  so  small,  that  in  a  cir- 
cle two  feet  in  diameter,  it  would  be  less  than  the 
two-hundredth  part  of  an  inch.  If  this  construction 
were  exact,  the  great  problem  would  have  been  solved. 

One  point,  however,  must  be  noted :  the  circle  is 
of  all  curved  lines  the  easiest  to  draw  by  mechanical 
means.  But  there  are  others  which  can  be  so  drawn. 
And,  if  such  curves  as  these  be  admitted  as  available, 
the  problem  of  the  quadrature  of  the  circle  can  be 
readily  solved.  There  is  a  curve,  for  instance,  in- 
vented by  Dinostratus  which  can  readily  be  described 
mechanically,  and  has  been  called  the  quadratrix  of 
Dinostratus,  because  it  has  the  property  of  thus  solv- 
ing the  problem  we  are  dealing  with. 

As  such  curves  can  be  described  with  quite  as 
much  accuracy  as  the  circle — for,  be  it  remembered, 
an  absolutely  perfect  circle  has  never  yet  been  drawn 
— we  see  that  it  is  only  the  limitations  which  geome- 
ters have  themselves  invented  that  give  this  problem 
its  difficulty.  Its  solution  has,  as  we  have  said,  no 
value ;  and  no  mathematician  would  ever  think  of 


324  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

wasting  a  moment  over  the  problem — for  this  reason, 
simply,  that  it  has  long  since  been  demonstrated  to 
be  insoluble  by  simple  geometrical  methods.  So  that, 
when  a  man  says  he  has  squared  the  circle  (and  many 
will  say  BO,  if  one  will  only  give  them  a  hearing),  he 
shows  that  either  he  wholly  misunderstands  the  nature 
of  the  problem,  or  that  his  ignorance  of  mathematics 
has  led  him  to  mistake  a  faulty  for  a  true  solution. 

(From  CJiambertfs  Journal^  January  16,  1869.) 


THE  NEW  THEORY  OF  ACHILLE&S  SHIELD. 

A  DISTINGUISHED  classical  authority  has  remarked 
that  the  description  of  Achilles's  shield  occupies  an 
anomalous  position  in  Homer's  "  Iliad."  On  the  one 
hand,  it  is  easy  to  show  that  the  poem — for  the  descrip- 
tion may  be  looked  on  as  a  complete  poem — is  out  of 
place  in  the  "  Iliad ; "  on  the  other,  it  is  no  less  easy  to 
show  that  Homer  has  carefully  led  up  to  the  descrip- 
tion of  the  shield  by  a  series  of  introductory  events. 

I  propose  to  examine,  briefly,  the  evidence  on  each 
of  these  points,  and  then  to  exhibit  a  theory  respecting 
the  shield  which  may  appear  bizarre  enough  on  a  first 
view,  but  which  seems  to  me  to  be  supported  by  satis- 
factory evidence. 

An  argument  commonly  urged  against  the  genuine- 
ness of  the  "  Shield  of  Achilles "  is  founded  on  the 


THE  NEW  THEORY   OF  ACHILLES'S  SHIELD.         325 

length  and  labored  character  of  the  description.  Even 
Grote,  whose  theory  is  that  Homer's  original  poem  was 
not  an  Iliad.,  but  an  A.chilleis^  has  admitted  the  force 
of  this  argument.  He  finds  clear  evidence  that  from 
Book  II.  to  Book  XX.,  Homer  has  been  husbanding 
his  resources  for  the  more  effective  description  of  the 
final  conflict.  He  therefore  concedes  the  possibility 
that  the  "  Shield  of  Achilles  "  may  be  an  interpolation 
— perhaps  the  work  of  another  hand. 

It  appears  to  me,  however,  that  the  mere  length  of 
the  description  is  no  argument  against  the  genuineness 
of  the  passage.  Events  have,  indeed,  been  hastening 
to  a  crisis  up  to  the  end  of  Book  XYIL,  and  the  action 
is  checked  in  a  marked  manner  by  the  '  Oplopoeia  "  in 
Book  XYIII.  Yet  it  is  quite  in  Homer's  manner  to 
introduce,  between  two  series  of  important  events,  an 
interval  of  comparative  inaction,  or  at  least  of  events 
wholly  different  in  character  from  those  of  either  series. 
"We  have  a  marked  instance  of  this  in  Books  IX.  and 
X.  Here  the  appeal  to  Achilles  and  the  night-adven- 
ture of  Diomed  and  Ulysses  are  interposed  between 
the  first  victory  of  the  Trojans  and  the  great  struggle 
in  which  Patroclus  is  slain,  and  Agamemnon,  Ulysses, 
Diomed,  Machaon,  and  Eurypylus  wounded.*  In  fact 

*  Another  well-known  instance,  where  "Patroclus  sent  in  hot  haste 
for  news  by  a  man  of  the  most  fiery  impatience,  is  button-held  by  Nes- 
tor, and  though  he  has  no  time  to  sit  down,  yet  is  obliged  to  endure 
a  speech  of  152  lines,"  is  accounted  for  by  Gladstone  in  a  different 
manner. 


326  LIGHT  SCIEXCE  FOR  LEISURE  HOURS. 

one  cannot  doubt  that  in  such  an  arrangement  Homer 
exhibits  admirable  taste  and  judgment.  The  contrast 
between  action  and  inaction,  or  between  the  confused 
tumult  of  a  heady  conflict  and  the  subtle  advance  of 
the  two  Greek  heroes,  is  conceived  in  the  true  poetic 
spirit.  The  dignity  and  importance  of  the  action,  and 
the  interest  of  the  interposed  events,  are  alike  en- 
hanced. Indeed,  there  is  scarcely  a  noted  author 
whose  works  do  not  afford  instances  of  corresponding 
contrasts.  How  skilfully,  for  example,  has  Shake- 
speare interposed  the  "  bald,  disjointed  chat "  of  the 
sleepy  porter  between  the  conscience-wrought  horror 
of  Duncan's  murderers  and  the  "  horror,  horror,  hor- 
ror "  which  "  tongue  nor  heart  could  not  conceive  nor 
name"  of  his  faithful  followers.  Nor  will  the  reader 
need  to  be  reminded  of  the  frequent  and  effective  use 
by  Dickens  of  the  contrast  between  the  humorous  and 
the  pathetic. 

The  labored  character  of  the  description  of  the 
shield  is  an  argument — though  not,  perhaps,  a  very 
striking  one — of  the  independent  origin  of  the  poem. 

But  the  arguments  on  which  I  am  disposed  to  lay 
most  stress  lie  nearer  the  surface. 

Scarcely  any  one,  I  think,  can  have  read  the  de- 
scription of  the  shield  without  a  feeling  of  wonder  that 
Homer  should  describe  the  shield  of  a  mortal  hero  as 
adorned  with  so  many  and  such  important  objects. 
We  find  the  sun  and  moon,  the  constellations,  the  waves 


THE  NEW   THEORY   OF  ACHILLES'S  SHIELD.         827 

of  ocean,  and  a  variety  of  other  objects,  better  suited  to 
adorn  the  temple  of  a  great  deity  than  the  shield  of  a 
warrior,  however  noble  and  heroic.  The  objects  de- 
picted even  on  the  ^Egis  of  Zeus  are  much  less  impor- 
tant. There  is  certainly  no  trace  in  the  "  Iliad  "  of  a 
wish  on  Homer's  part  to  raise  the  dignity  of  mortal 
heroes  at  the  expense  of  Zeus,  yet  the  .zEgis  is  thus 
succinctly  described : 

"Fringed  round  with  ever-fighting  snakes,  though  it  was  drawn 

to  life 

The  miseries- and  deaths  of  fight;  in  it  frowned  hloody  Strife, 
In  it  shone  sacred  Fortitude,  in  it  fell  Pursuit  flew, 
In  it  the  monster  Gorgon's  head,  in  which  held  out  to  view 
Were  all  the  dire  ostents  of  Jove." — Chapman's  Translation. 

Five  lines  here,  as  in  the  original,  suffice  for  the 
description  of  Jove's  ^Egis,  while  one  hundred  and 
thirty  lines  are  employed  in  the  description  of  the 
celestial  and  terrestrial  objects  depicted  on  the  shield 
of  Achilles. 

Another  circumstance  attracts  notice  in  the  descrip- 
tion of  Achilles's  armor — the  disproportionate  impor- 
tance attached  to  the  shield.  Undoubtedly,  the  shield 
wras  that  portion  of  a  hero's  armor  which  admitted  of 
the  freest  application  of  artistic  skill.  Yet  this  con- 
sideration is  not  sufficient  to  account  for  the  fact  that, 
while  so  many  lines  are  given  to  the  shield,  the  helmet, 
corselet,  and  greaves,  are  disposed  of  in  four. 

But  the  argument  on  which  I  am  inclined  to  lay 
most  stress  is  the  occurrence  elseichcre  of  a  description 


328  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

which  is  undoubtedly  only  another  version  of  the 
"Shield  of  Achilles."  The  "Shield  of  Hercules" 
occurs  in  a  poem  ascribed  to  Hesiod.  But  whatever 
opinion  may  be  formed  respecting  the  authorship  of 
the  description,  there  can  be  no  doubt  that  it  is  not 
Hesiod's  work.  It  exhibits  no  trace  of  his  dry,  didac- 
tic, somewhat  heavy  style.  Elton  ascribes  the  "  Shield 
of  Hercules  "  to  an  imitator  of  Homer,  and  in  support 
of  this  view  points  out  those  respects  in  which  the 
poem  resembles,  and  those  in  which  it  is  inferior  to, 
the  "  Shield  of  Achilles."  The  two  descriptions  are, 
however,  absolutely  identical  in  many  places ;  and  this 
would  certainly  not  have  happened  if  one  had  been  an 
honest  imitation  of  the  other.  And  those  parts  of  the 
"  Shield  of  Hercules  "  which  have  no  counterparts  in 
the  "  Shield  of  Achilles  "  are  too  well  conceived  and 
expressed  to  be  ascribed  to  a  very  inferior  poet — a  poet 
so  inferior  as  to  be  reduced  to  the  necessity  of  simply 
reproducing  Homer's  words  in  other  parts  of  the  poem. 
Those  parts  which  admit  of  comparison — where,  for 
instance,  the  same  objects  are  described,  but  in  differ- 
ent terms — are  certainly  inferior  in  the  "  Shield  of 
Hercules."  The  description  is  injured  by  the  addition 
of  unnecessary  or  inharmonious  details.  Elton  speaks, 
accordingly,  of  these  portions  as  if  they  were  expan- 
sions of  the  corresponding  parts  of  the  "  Shield  of 
Achilles."  This  appears  to  me  a  mistake.  It  seems 
far  more  likely  that  both  descriptions  are  by  the  same 


THE  NEW  THEORY  OF  ACHILLES'S  SHIELD.         329 

poet.  It  is  not  necessary  for  the  support  of  my  theory 
that  this  poet  should  be  Homer,  but  I  think  both  de- 
scriptions show  undoubted  traces  of  his  handiwork. 
Indeed,  all  known  imitations  of  Homer  are  so  easily 
recognizable  as  the  work  of  inferior  poets,  that  I  should 
have  thought  no  doubt  could  exist  on  this  point,  but 
for  the  attention  which  the  German  theory  respecting 
the  "  Iliad  "  has  received.  Assigning  both  poems  to 
Homer,  the  "  Shield  of  Hercules  "  may  be  regarded, 
not  as  an  expansion  (in  parts)  of  the  "Shield  of 
Achilles,"  but  as  an  earlier  work  of  Homer's,  improved 
and  pruned  by  his  maturer  judgment,  when  he  desired 
to  fit  it  into  the  plan  of  the  "  Iliad."  Or  rather,  each 
poem  may  be  looked  on  as  an  abridgment  (the  "  Shield 
of  Hercules  "  the  earlier)  of  an  independent  work  on  a 
subject  presently  to  be  mentioned. 

It  is  next  to  be  shown  that,  in  the  events  preceding 
the  "  Oplopoeia,"  there  is  a  preparation  for  the  intro- 
duction of  a  separate  poem. 

In  the  first  place,  every  reader  of  Homer  is  familiar 
with  the  fact  that  the  poet  constantly  makes  use,  when 
occasion  serves,  of  expressions,  sentences,  often  even 
of  complete  passages,  which  have  been  already  applied 
in  a  corresponding,  or  occasionally  even  in  a  wholly 
different,  relation.  The  same  epithets  are  repeatedly 
applied  to  the  same  deity  or  hero.  A  long  message  is 
delivered  in  the  very  words  which  have  been  already 
used  by  the  sender  of  the  message.  In  one  well-known 


330  LIGHT   SCIENCE  FOR  LEISURE  HOURS. 

instance  (in  Book  II.),  not  only  is  a  message  delivered 
thus,  but  the  person  who  has  received  it  repeats  it  to 
others  in  precisely  the  same  terms.  In  the  combat 
between  Hector  and  Ajax  (Book  VI.)?  the  flight  of 
Ajax's  spear,  and  the  movement  by  which  Hector 
avoids  the  missile;  are  described  in  six  lines,  differing 
only  as  to  proper  names  from  those  which  had  been 
already  used  in  describing  the  encounter  between  Paris 
and  Menelaus  (Book  III.). 

This  peculiarity  would  be  a  decided  blemish  in  a 
written  poem.  Tennyson,  indeed,  occasionally  copies 
Homer's  manner — for  instance,  in  "  Enid,"  he  twice 
repeats  the  line — 

"  As  careful  robins  eye  the  delver's  .toil ;  " 
but  with  a  good  taste  which  prevents  the  repetition 
from  becoming  offensive.  The  fact  is,  that  the  pe- 
culiarity marks  Homer  as  the  singer,  not  the  writer, 
of  poetry.  I  would  not  be  understood  as  accepting 
the  theory,  according  to  which  the  u  Iliad  "  is  a  mere 
string  of  ballads.  I  imagine  that  no  one  wrho  justly 
appreciates  that  noble  poem  would  be  willing  to 
countenance  such  a  theory.  But  that  the  whole  poem 
was  sung  by  Homer  at  those  prolonged  festivals  which 
formed  a  characteristic  peculiarity  of  Achaian  manners 
seems  shown,  not  only  by  what  we  learn  respecting 
the  later  "  rhapsodists,"  but  by  the  internal  evidence 
of  the  poem  itself.* 

*  Besides  Homer's  reference,  both  in  the  "  Iliad  "  and  the  "  Odyssey," 
to  poetic  recitations  at  festivals,  there  is  the  well-known  invocation  in 


THE  NEW  THEORY  OF  ACHILLES'S  SHIELD.         331 

Homer,  reciting  a  long  and  elaborate  poem  of  his 
own  composition,  occasionally  varying  the  order  of 
events,  or  adding  new  episodes,  extemporized  as  the 
song  proceeded,  would  exhibit  the  peculiarity  in- 
variably observed  in  the  "improvisator,"  of  using, 
more  than  once,  expressions,  sentences,  or  passages, 
which  happened  to  be  conveniently  applicable.  The 
art  of  extemporizing  depends  on  the  capacity  for  com- 
posing fresh  matter  while  the  tongue  is  engaged  in 
the  recital  of  matter  already  composed.  Any  one  who 
has  watched  a  clever  improvisator  cannot  fail  to  have 
noticed  that,  though  gesture  is  aptly  wedded  to  words, 
the  thoughts  are  elsewhere.  In  the  case,  therefore,  of 
an  improvisator,  or  even  of  a  rhapsodist  reciting  from 
memory,  the  occasional  recurrence  of  a  well-worn 
form  of  words  serves  as  a  relief  to  the  strained  inven- 
tion or  memory. 

We  have  reason,  then,  for  supposing  that  if  Homer 
had,  in  his  earlier  days,  composed  a  poem  which  was 
applicable,  with  slight  alterations,  to  the  story  of  the 
"  Iliad,"  he  would  endeavor,  by  a  suitable  arrangement 
of  the  plan  of  his  narrative,  to  introduce  the  lines 
whose  recital  had  long  since  become  familiar  to  him. 

Evidence  of  design  in  the  introduction  of  the 
"  Shield  of  Achilles  "  certainly  does  not  seem  wanting. 

Book  II.  To  what  purpose  would  the  mere  writer  of  poetry  pray  for 
an  increase  of  his  physical  powers  ?  Nothing  could  be  more  proper, 
says  Gladstone,  if  Homer  were  about  to  write ;  nothing  less  proper  if  he 
were  engaged  on  a  written  poem. 


332  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

It  is  "by  no  means  necessary  to  the  plot  of  tho 
"  Iliad  "  that  Achilles  should  lose  the  celestial  armor 
given  to  Peleus  as  a  dowry  with  Thetis.  On  the 
contrary,  Homer  has  gone  out  of  his  way  to  render 
the  labors  of  Yulcan  necessary.  Patroclus  has  to  be 
so  ingeniously  disposed  of,  that  while  the  armor  lie 
had  worn  is  seized  by  Hector,  his  body  is  rescued,  as 
are  also  the  horses  and  chariot  of  Achilles. 

We  have  the  additional  improbability  that  the 
armor  of  the  great  Achilles  should  fit  the  inferior 
warriors  Patroclus  and  Hector.  Indeed,  that  the 
armor  should  fit  Hector,  or  rather,  that  Hector  should 
fit  the  armor,  the  aid  of  Zeus  and  Ares  has  to  be 
called  in : 

"  To  this  Jove's  sable  brows  did  bow ;  and  lie  made  fit  his  limbs 
To  those  great  arms,  to  fill  which  up  the  war-god  entered  him 
Austere  and  terrible,  his  joints  and  every  part  extends 
With  strength  and  fortitude." — Chapman's  Translation. 

It  is  clear  that  the  narrative  would  not  have  been 
impaired  in  any  way,  while  its  probability  and  con- 
sistency would  have  been  increased,  if  Patroclus  had 
fought  in  his  own  armor.  The  death  of  Patroclus 
would  in  any  case  have  been  a  cause  sufficient  to 
arouse  the  wrath  of  Achilles  against  Hector — though 
certainly  the  hero's  grief  for  his  armor  is  nearly  as 
poignant  as  his  sorrow  for  his  friend's  death. 

It  appears  probable,  then,  that  the  description  of 
Achilles's  Shield  is  an  interpolation — the  poet's  own 


THE  NEW  THEORY  OF  ACIIILLES'S  SHIELD.         333 

work,  however,  and  brought  in  by  him  in  the  only 
way  he  found  available.  The  description  clearly  re- 
fers to  the  same  object  which  is  described  (here,  also, 
only  in  part)  in  the  "  Shield  of  Hercules."  The 
original  description,  doubtless,  included  all  that  is 
found  in  both  "  shields,"  and  probably  much  more. 

"What,  then,  was  the  object  to  which  the  original 
description  applied  ?  An  object,  I  should  think,  far 
more  important  than  a  warrior's  shield.  I  imagine 
that  any  one  who  should  read  the  description  with- 
out being  aware  of  its  accepted  interpretation  would 
consider  that  the  poet  was  dealing  with  an  important 
series  of  religious  sculptures,  possibly  that  he  was  de- 
scribing the  dome  of  a  temple  adorned  with  celestial 
and  terrestrial  symbols. 

In  Egypt  there  are  temples  of  a  vast  antiquity, 
having  a  dome,  on  which  a  zodiac — or,  more  correctly, 
a  celestial  hemisphere — is  sculptured  with  constella- 
tion-figures. And  we  now  learn,  from  ancient  Baby- 
lonian and  Assyrian  sculptures,  that  these  Egyptian 
zodiacs  are  in  all  probability  merely  copies  (more  or 
less  perfect)  of  yet  more  ancient  Chaldean  zodiacs. 
One  of  these  Babylonian  sculptures  is  figured  in 
Rawlinson's  "Ancient  Monarchies."  It  seems  prob- 
able that  in  a  country  where  Sabaeanism,  or  star-wor- 
ship, was  the  prevailing  form  of  religion,  yet  more 
imposing  proportions  would  be  given  to  such  zodiacs 
than  in  Egypt. 


334  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

My  theory,  then,  respecting  the  Shield  of  Achilles 
is  this : 

I  conceive  that  Homer,  in  his  Eastern  travels, 
visited  imposing  temples  devoted  to  astronomical  ob- 
servation  and  star-worship ;  and  that  nearly  every 
line  in  both  "  shields  "  is  borrowed  from  a  poem  in 
which  he  described  a  temple  of  this  sort,  its  domed 
zodiac,  and  those  illustrations  of  the  labors  of  differ- 
ent seasons  and  of  military  or  judicial  procedures 
which  the  astrological  proclivities  of  star-worshippers 
led  them  to  associate  with  the  different  constellations. 

I  think  there  are  arguments  of  some  force  to  be 
urged  in  support  of  this  theory,  fanciful  as  it  may 
seem. 

In  the  first  place,  it  is  necessary  that  the  constella- 
tions recognized  in  Homer's  time  (not  necessarily,  or 
probably,  l>y  Homer)  should  be  distinguished  from 
later  inventions. 

Aratus,  writing  long  after  Homer's  date,  mentions 
forty-five  constellations.  These  were  probably  derived, 
without  exception,  from  the  globe  of  Eudoxus.  Re- 
membering the  tendency  which  astronomers  have 
shown,  in  all  ages,  to  add  to  the  list  of  constellations, 
we  may  assume  that  in  Homer's  time  the  number 
was  smaller.  Probably  there  were  some  fifteen  north- 
ern and  ten  southern  constellations,  besides  the  twelve 
zodiacal  signs.  The  smaller  constellations  mentioned 
by  Aratus  doubtless  formed  parts  of  larger  figures. 


THE  NEW   THEORY  OF  ACHILLES'S  SHIELD.         335 

Any  one  wlio  studies  the  heavens  will  recognize  the 
fact  that  the  larger  constellations  have  been  robbed 
of  their  just  proportions  to  form  the  smaller  asterisms. 
Corona  Borealis  was  the  right  arm  of  Bootes,  Ursa 
Minor  was  a  wing  of  Draco  (now  wingless,  and  no 
longer  a  dragon),  and  so  on. 

Secondly,  it  is  necessary  that  the  actual  appearance 
of  the  heavens,  with  reference  to  the  position  of  the 
pole  in  Homer's  time,  should  be  indicated.  For  our 
present  purpose,  it  is  not  necessary  that  we  should 
know  the  exact  date  at  which  the  most  ancient  of  the 
zodiac-temples  were  constructed  (or  to  which  they 
were  made  to  correspond).  There  are  good  reasons, 
though  this  is  not  the  proper  place  for  dwelling  upon 
them,  for  supposing  that  the  great  epoch  of  reference 
among  ancient  astronomers  preceded  the  Christian  era 
by  about  2,200  years.  Be  this  as  it  may,  any  epoch 
between  the  date  named  and  the  probable  date  at 
which  Homer  flourished — say  nine  or  ten  centuries 
before  the  Christian  era — will  serve  equally  well  for 
our  present  purpose.  Now,  if  the  effects  of  equi- 
noctial precession  be  traced  back  to  such  a  date,  we 
are  led  to  notice  two  singular  and  not  uninteresting 
circumstances.  First,  the  pole  of  the  heavens  fell  in 
the  central  part  of  the  great  constellation  Draco ;  and, 
secondly,  the  equator  fell  along  the  length  of  the  great 
sea-serpent,  Hydra,  in  one  part  of  its  course,  and  else- 
where to  the  north  of  all  the  ancient  aquatic  constella- 


336  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

tions,*  save  that  one-half  of  the  northernmost  fish 
(of  the  zodiac  pair)  lay  north  of  the  equator.  Thus, 
if  a  celestial  sphere  were  constructed  with  the  equator 
in  a  horizontal  position,  the  Dragon  would  be  at  the 
summit,  Hydra  would  be  extended  horizontally  along 
the  equator  —  but  with  his  head  and  neck  reared 
above  that  circle  —  and  Argo,  Cetus,  Capricornus, 
Piscis  Australis,  and  Pisces  —  save  one-half  of  the 
northernmost — would  lie  Mow  the  equator.  It  may, 
also,  be  mentioned  that  all  the  bird-constellations 
were  then,  as  now,  clustered  together  not  far  from 
the  equator — Cygnus  (the  farthest  from  the  equator) 
being  ten  degrees  or  so  nearer  to  that  circle  than  at 
present. 

Now  let  us  turn  to  the  two  "shields,"  and  see 
whether  there  is  any  thing  in  them  to  connect  them 
with  zodiac-temples,  or  to  remind  us  of  the  relations 
exhibited  above.  To  commence  with  the  "  Shield  of 
Achilles,"  the  opening  lines  inform  us  that  there  ap- 
peared— 

"  The  starry  lights  that  heaven's  high  convex  crowned, 
The  Pleiads,  Hyads,  with  the  northern  team, 
And  great  Orion's  more  refulgent  beam." 

And  here,  in  Achilles's  shield,  the  list  of  constellations 
closes ;  but  it  is  remarkable  that  in  the  "  Shield  of 
Hercules,"  while  the  above  lines  are  wanting,  we  find 

*  We  may  exclude  Delphinus  as  probably  later  than  Homer's  time, 
though  mentioned  by  Aratus. 


THE  NEW   THEORY   OF  ACHILLES'S  SHIELD.          337 

lines  which  clearly  point  to  other  constellations.  [Re- 
membering what  has  just  been  stated  about  Draco, 
it  seems  at  the  least  a  singular  coincidence  that  we 
should  find  the  centre  or  boss  of  the  shield  occupied 
by  a  dragon  : 

"  The  scaly  horror  of  a  dragon,  coiled 
Full  in  the  central  field,  unspeakable, 
With  eyes  oblique  retorted,  that  aslant 
Shot  gleaming  flame."* — Elton's  Translation. 

We  seem,  also,  to  find  a  reference  to  the  above-named 
relations  of  the  aquatic  constellations,  and  specially  to 
the  constellation  Pisces  : 

"  In  the  midst, 

Full  many  dolphins  chased  the  fry,  and  sho\ved 
As  though  they  swam  the  waters,  to  and  fro 
Darting  tumultuous :  two  t  of  silver  scale 
Panting  above  the  wave." 

*  Compare  the  description  of  the  constellation  Draco  by  Aratus : 

"  Swol'n  is  his  neck — eyes  charged  with  sparkling  fire 
His  crested  head  illume.     As  if  in  ire 
To  Helice  he  turns  his  foaming  jaw 
And  darts  his  tongue,  barbed  with  a  blazing  star." 

LamVs  Translation. 

f  It  is  scarcely  necessary  to  remark  that  no  importance  is  to  be 
attached  to  the  numerical  relations  in  this  and  other  passages.  In  the 
original  work  describing  a  zodiac-dome,  the  exact  number  of  constella- 
tions representing  fishes,  dogs,  or  the  like,  would  of  course  be  men- 
tioned ;  but  any  changes  necessary  to  Homer's  purpose  in  describing  a 
shield  would  unhesitatingly  have  been  introduced  by  him  subsequently. 
It  is  singular,  however,  that  we  should  have  here,  and  in  the  passage 
quoted  farther  on  as  referring  to  Orion  and  the  Dogs,  the  number  two 

15 


338  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

For  we  learn  from  both  "  shields  "  that  the  waves  of 
ocean  were  figured  in  a  position  corresponding  with 
the  above-mentioned  position  of  the  celestial  equator, 
beneath  which — that  is,  in  the  ocean,  on  our  assump- 
tion— the  aquatic  constellations  were  figured.  The 
description  of  the  ocean  in  the  "  Shield  of  Hercules  " 
contains  also  some  lines,  in  which  we  seem  to  see  a 
reference  to  the  bird-constellations  close  above  the 
equator : 

"Rounding  the  utmost  verge  the  ocean  flowed 
As  in  full  swell  of  waters,  and  the  shield 
All  variegated  with  whole  circle  bound. 
Swans  of  high-hovering  wing  there  clamored  shrill, 
Who  also  skimmed  the  breasted  surge  with  plume 
Innumerous  ;  near  them  fishes  'midst  the  waves 
Frolicked  in  wanton  bounds." 

In  the  "  Shield  of  Achilles  "  no  mention  is  made  of 
Perseus,  but  in  the  "  Shield  of  Hercules  "  this  well- 
known  constellation  seems  described  in  the  lines — 

"  There  was  the  knight  of  fair-haired  Danae  born, 
Perseus ;  nor  yet  the  buckler  with  his  feet 
Touched  nor  yet  distant  hovered,  strange  to  see, 
For  nowhere  on  the  surface  of  the  shield 
He  rested  ;  so  the  crippled  artist-god 

specially  mentioned.  The  latter  instance  is  -the  more  remarkable,  inas- 
much as  the  mention  of  men  and  hares  would  lead  one  to  expect  that 
more  than  two  dogs  would  be  introduced.  I  would  suggest  as  a  suffi- 
cient reason  for  this  peculiarity  that  the  verbal  alterations  necessary  to 
pluralize  some  of  the  objects  in  the  dome  would  be  more  easily  effected 
than  those  necessary  to  undualize  others. 


THE  NEW  THEORY  OF  ACHILLES'S  SHIELD.         339 

Illustrious  framed  him  with  his  hands  in  gold. 
Bound  to  his  feet  were  sandals  winged  ;  a  sword 
Of  brass,  with  hilt  of  sable  ebony, 
Hung  round  him  from  the  shoulders  by  a  thong. 

The  visage  grim 

Of  monstrous  Gorgon  all  his  back  o'erspread ; 

the  dreadful  helm 

Of  Pluto  clasped  the  temples  of  the  prince." 

I  tliink  tliat  one  may  recognize  a  reference  to  the 
twins  Castor  and  Pollux  (the  wrestler  and  boxer  of 
mythology)  in  the  words — 

"But  in  another  part 

Were  men  who  wrestled,  or  in  gymnic  fight 
Wielded  the  cestus." 

Orion  is  not  mentioned  by  name  in  the  "  Shield  of 
Hercules,"  as  in  the  other ;  but  Orion,  Lepus,  and  the 
two  dogs,  seem  referred  to : 

"Elsewhere  men  of  chase 

Were  taking  the  fleet  hares ;  two  keen-toothed  dogs 
Bounded  beside,  these  ardent  in  pursuit, 
Those  with  like  ardor  doubling  in  their  flight." 

In  each  "shield"  we  find  a  reference  to  the  opera- 
tions of  the  year — hunting  and  pasturing,  sowing, 
ploughing,  and  harvesting.  It  is  hardly  necessary  to 
point  out  the  connection  between  these  operations  and 
astronomical  relations.  That  this  connection  was  fully 
recognized  in  ancient  times  is  shown  in  the  "  Works 
and  Days"  of  Hesiod.  "We  find  also  in  Egyptian 


340  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

zodiacs  clear  evidence  that  these  operations,  as  well  as 
astronomical  symbols  or  constellations,  found  a  record 
in  sculptured  domes. 

The  judicial,  military,  and  other  proceedings  de- 
scribed in  the  "  Shield  of  Achilles  "  were  also  sup- 
posed by  the  ancients  to  have  been  influenced  by  the 
courses  of  the  stars. 

If  we  had  no  evidence  that  ancient  celestial  spheres 
presented  the  constellations  above  referred  to,  we 
might  be  disposed  to  attach  less  weight  to  the  coinci- 
dences here  presented;  but  the  "Phenomena"  of 
Aratus  affords  sufficient  testimony  on  this  point.  In 
the  first  place,  that  work  is  of  great  antiquity,  since 
Aratus  flourished  two  centuries  and  a  half  before  the 
Christian  era ;  but  it  is  well  known  that  Aratus  did 
not  describe  the  results  of  his  own  observations.  The 
positions  of  the  constellations,  as  recorded  by  him, 
accord  neither  with  the  date  at  which  he  wrote  nor 
with  the  latitude  in  which  he  lived.  It  is  generally 
assumed — chiefly  on  the  authority  of  Hipparchus — 
that  Aratus  borrowed  his  knowledge  of  astronomy 
from  the  sphere  of  Eudoxus ;  but  we  must  go  much 
farther  back  even  than  the  date  of  Eudoxus,  before  we 
can  find  any  correspondence  between  the  appearance 
of  the  heavens  and  the  description  given  by  Aratus. 
Thus  we  may  very  fairly  assume  that  the  origin  of  the 
constellations  (as  distinguished  from  their  association 
with  certain  circles  of  tho  celestial  sphere)  may  be 


THE  NEW  THEORY  OF  ACHILLES'S  SHIELD.         341 

placed  at  a  date  preceding,  perhaps  by  many  genera- 
tions, that  at  which  Homer  flourished. 

Indeed,  there  have  not  been  wanting  those  who  find 
in  the  ancient  constellations  the  record  of  the  early 
history  of  man.  According  to  their  views,  Orion  is 
Mmrod — the  "  Giant,"  as  the  Arabic  name  of  the  con- 
stellation implies — the  mighty  hunter,  as  the  dogs  and 
hare  beside  him  signify.  The  Centaur  bearing  a 
victim  toward  the  altar  is  Noah ;  Argo,  the  stern  of  a 
ship,  is  the  ark,  as  of  old  it  might  be  seen  on  Mount 
Ararat.  Corvus  is  the  crow  sent  forth  by  Noah,  and 
the  bird  is  placed  on  Hydra's  back  to  show  that  there 
was  no  land  on  which  it  could  set  its  foot.  The  figure 
now  called  Hercules,  but  of  old  Engonasin,  or  the 
kneeler,  and  described  by  Aratus  as  "  a  man  doomed 
to  labor,"  is  Adam.  His  left  foot  treads  on  the 
dragon's  head,  in  token  of  the  saying,  "  It  shall  bruise 
thy  head ; "  and  Serpentarius,  or  the  serpent-bearer,  is 
the  promised  seed. 

Of  course,  if  we  accept  these  views,  we  have  no 
difficulty  in  understanding  that  a  poet  so  ancient  as 
Homer  should  refer  to  the  constellations  which  still 
appear  upon  celestial  spheres.  And,  in  any  case,  the 
mere  question  of  antiquity  presents,  as  we  have  already 
shown,  little  difficulty. 

But  there  is  a  difficulty  in  one  respect,  a  notice 
of  which  must  close  this  paper,  already  carried  far  be 
yond  the  limits  I  had  proposed  to  myself:  It  may  be 


342  LIGHT  SCIENCE  FOR  LEISURE  HOURS. 

thought  remarkable  that  heroes  of  Greek  mythology, 
as  Perseus  and  Orion,  should  be  placed  by  Homer,  or 
even  by  Aratus,  in  spheres  which  are  undoubtedly  of 
Eastern  origin. 

ISTow,  it  may  be  remarked,  first,  of  Homer,  that  many 
acute  critics  consider  the  whole  story  of  the  "  Iliad  "  to 
be,  in  reality,  merely  an  adaptation  of  an  Eastren  nar- 
rative to  Greek  scenes  and  names.  It  is  pointed  out 
that,  whereas  the  Catalogue  in  Book  II.  reckons  up- 
ward of  100,000  men,  only  10,000  fought  at  Marathon ; 
and,  whereas  there  are  counted  no  less  than  1,200  ships 
in  the  Catalogue,  there  were  but  271  at  Artemisium, 
and  at  Salamis  but  378.  However  this  may  be,  we 
have  the  distinct  evidence  of  Herodotus  that  the  Greek 
mythology  was  derived  originally  from  foreign  sources. 
He  says,  "  All  the  names  of  the  gods  in  Greece  were 
brought  from  Egypt,"  an  opinion  in  which  Diodorus 
and  other  eminent  authorities  concur.  But  it  is  the 
opinion  of  acute  modern  critics  that  we  must  go 
beyond  Egyptian — to  Assyrian,  or  Indian,  perhaps  even 
to  Hebrew  sources,  for  the  origin  of  Greek  mythology. 
Bryant  traces  nearly  all  the  Greek  myths  to  traditions 
of  the  dispersion  of  the  Cuthites  or  Cuseans.  And 
Layard  has  ascribed  to  Niebuhr  the  following  signifi- 
cant remarks  :  "  There  is  a  want  in  Grecian  art  which 
neither  I,  nor  any  man  now  alive,  can  supply.  There 
is  not  enough  in  Egypt  to  account  for  the  peculiar  art 
and  the  peculiar  mythology  which  we  find  in  Greece. 


THE  NEW  TUEORY  OF  ACIIILLES'S  SHIELD.         343 

That  the  Egyptians  did  not  originate  it  I  ana  con- 
vinced, though  neither  I,  nor  any  man  now  alive, 
can  say  who  were  the  originators.  But  the  time  will 
come  when,  on  the  borders  of  the  Tigris  and  Euphra- 
tes, those  who  come  after  me  will  live  to  see  the 
origin  of  Grecian  art  and  Grecian  mythology." 

(From  The  Student,  June,  1868.) 


THE  END. 


THE  DESCENT  OF  MAN. 


The  Descent  of  Man, 

AND  SELECTION  IN  RELATION  TO  SEX.  By  CHARLES  DAR. 
WIN,  M.  A.,  F.  B.  S.,  etc.  With  Illustrations.  2  vols.,  12iuo.  Cloth. 
Price,  $2.00  per  vol. 

Origin  of  Species  &//  Means  of  Natural  Selection; 

Or,  the  Preservation  of  Favored  Races  in  the  Struggle  for  Life.  New 
and  revised  edition.  By  CHARLES  DARWIN,  M.  A.,  F.  R.  S.,  F.  G.  S., 
etc.  With  copious  Index.  1  vol.,  12mo.  Cloth.  Price,  $2.00. 

ST.  GKEOiRG-E   MilV^UT. 
On  the  Genesis  of  Species. 

By  ST.  GEORGE  MIVART,  F.R.  S.  12mo,  316  pages.  Illustrated. 
Cloth.  Price,  $1.75. 


The  Principles  of  Biology. 

By  HERBERT  SPENCER.     2  vols.     $5.CO. 


Marts  Place  in  Nature. 

By  THOMAS  H.   HUXLEY,  LL.D.,  F.R.S.      1  vol.,  12rao.      Cloth. 
"Price,  $1.25. 

On  the  Origin  of  Species. 

By  THOMAS  H.  HUXLEY,  LL.  D.,  F.  R.  S.  1  vol.,  12mo.  Cloth.  Price,  $1. 


Hereditary  Genius: 

An  Inquiry  into  its  Laws  and  Consequences.    By  FRANCIS  GALTON. 
New  revised  edition.     12mo.     Cloth.    Price,  $2.00, 


1'rimitive  Man. 

Illustrated  with  thirty  Scenes  of  Primitive  Life,  and  233  Figures  of 
Objects  belonging  to  Prehistoric  Ages.  By  Louis  FIGUIER,  author 
of  "  The  World  before  the  Deluge,"  "  The  Ocean  World,"  etc.  1 
vol.,  8vo.  Cloth.  Price,  $4.00. 

H.TJB33OCK. 
Origin  of  Civilization* 

AND  THE  PRIMITIVE  CONDITION  OF  MAN.  By  Sir  JOHN 
LUBBOCK,  Bart.,  M.  P.  1  vol.,  12mo.  Cloth.  Price,  $2.00. 


Either  of  the  above  mailed  to  any  address  within  the  United  States,  on 
receipt  of  price. 

D.  APPLETON  &  CO.,  Publishers, 

Nos.  649  &  651  BKOADWAY,  N.  Y. 


THE  ORIGIN  OF  CIVILIZATION; 

OR,  THE 

PRIMITIVE  CONDITION  OF  MAN. 
By  SIE   JOHN   LTTBBOCK,  Bart,  M.  P.,  F.  R.  S, 

38O    Tages.    Illustrated. 

This  interesting  work  is  the  fruit  of  many  years'  research 
by  an  accomplished  naturalist,  and  one  well  trained  in  mod- 
ern scientific  methods,  into  the  mental,  moral,  and  social  con- 
dition of  the  lowest  savage  races.  The  want  of  a  work  of 
this  kind  had  long  been  felt,  and,  as  scientific  methods  are 
being  more  and  more  applied  to  questions  of  humanity,  there 
has  been  increasing  need  of  a  careful  and  authentic- work  de- 
scribing the  conditions  of  those  tribes  of  men  who  are  lowest 
in  the  scale  of  development. 

"  This  interesting  work — for  it  is  intensely  so  in  its  aim,  scope,  and  the 
ability  of  its  author — treats  of  what  the  scientists  denominate  anthropology, 
or  the  natural  history  of  the  human  species ;  the  complete  science  of  man, 
body  and  soul,  including  sex,  temperament,  race,  civilization,  etc." — Provi- 
dence Press. 

"A  work  which  is  most  comprehensive  in  its  aim,  and  most  admirable  in 
its  execution.  The  patience  and  judgment  bestowed  on  the  book  are  every- 
where apparent ;  the  mere  list  of  authorities  quoted  giving  evidence  of  wide 
and  impartial  reading.  The  work,  indeed,  is  not  only  a  valuable  one  on  ac- 
count of  the  opinions  it  expresses,  but  it  is  also  most  serviceable  as  a  book 
of  reference.  It  offers  an  able  and  exhaustive  table  of  a  vast  array  of  facts, 
which  no  single  student  could  well  obtain  for  himself,  and  it  has  not  been 
made  the  vehicle  for  any  special  pleading  on  the  part  of  the  author."— 
London  Athenaeum. 

11  The  book  is  no  cursory  and  superficial  review ;  it  goes  to  the  very  heart 
of  the  subject,  and  embodies  the  results  of  all  the  later  investigations.  It  ia 
replete  with  curious  and  quaint  information  presented  in  a  compact,  luminous, 
and  entertaining  form." — Albany  Evening  Journal. 

41  The  treatment  of  the  subject  is  eminently  practical,  dealing  more  with 
fact  than  theory,  or  perhaps  it  will  be  more  just  to  say,  dealing  only  with 
theory  amply  sustained  by  fact." — Detroit  Free  Press. 

"This  interesting  and  valuable  volume  illustrates,  to  some  extent,  the 
way  in  which  the  modern  scientific  spirit  manages  to  extract  a  considerable 
treasure  from  the  chaff  and  refuse  neglected  or  thrown  aside  by  former  in 
quirers." — London  Saturday  Jteview. 

D.  APPLETON  &  CO.,  Publishers. 


J).  Appleton  &  Company's 

LAY   SERMONS, 
ADDKESSES,    AND    REVIEWS, 

BY  THOMAS  HENRY  HUXLEY. 
Cloth,  12mo.      390  pages.      Price,  $1.75 

THIS  is  the  latest  and  most  popular  of  the  works  of  this  in- 
itrepid  and  accomplished  English  thinker.  The  American  edition 
of  the  work  is  the  latest,  and  contains,  in  addition  to  the  English 
edition,  Professor  Huxley's  recent  masterly  address  on  "  Spon- 
taneous Generation,"  delivered  before  the  British  Association  for 
the  Advancement  of  Science,  of  which  he  was  president. 
The  following  is  from  an  able  article  in  the  Independent  : 

The  "  Lay  Sermons,  Addresses,  and  Reviews  "  is  a  book  to  be  read 
by  every  one  who  would  keep  up  with  the  advance  of  truth — as  well  by 
those  who  are  hostile  as  those  who  are  friendly  to  his  conclusions.  In 
it,  scientific  and  philosophical  topics  are  handled  with  consummate  abil- 
ity. It  is  remarkable  for  purity  of  style  and  power  of  expression.  No- 
where, in  any  modern  work^  is  the  advancement  of  the  pursuit  of  that 
natural  knowledge,  which  is  of  vital  importance  to  bodily  and  mental 
well-being,  so  ably  handled. 

Professor  Huxley  is  undoubtedly  the  representative  scientific  man  of 
the  age.  His  reverence  for  the  right  and  devotion  to  truth  have  estab- 
lished his  leadership  of  modern  scientific  thought.  He  leads  the  beliefs 
and  aspirations  of  the  increasingly  powerful  body  of  the  younger  men  of 
science.  His  ability  for  research  is  marvellous.  There  is  possible  no  more 
equipoise  of  judgment  than  that  to  which  he  brings  the  phenomena  of 
Nature.  Besides,  he  is  not  a  mere  scientist.  His  is  a  popularized  phi. 
losophy  ;  social  questions  have  been  treated  by  his  pen  in  a  manner  most 
masterly.  In  his  popular  addresses,  embracing  the  widest  range  of  top- 
ics, he  treads  on  ground  with  which  he  seems  thoroughly  familiar. 

There  are  those  who  hold  the  name  of  Professor  Huxley  as  synony. 
mous  with  irreverence  and  atheism.  Plato's  was  so  held,  and  Galileo't, 
and  Descartes's,  and  Newton's,  and  Faraday's.  There  can  be  no  greatei 
mistake.  No  man  has  greater  reverence  for  the  Bible  than  Huxley.  Nc 
one  more  acquaintance  with  the  text  of  Scripture.  He  believes  there  is 
definite  government  of  the  universe  ;  that  pleasures  and  pains  are  distrib- 
uted in  accordance  with  law  ;  and  that  the  certain  proportion  of  evil 
woven  up  in  the  life  even  of  worms  will  help  the  man  \vho  thinks  to  bear 
his  own  share  with  courage. 

In  the  estimate  of  Professor  Huxley's  future  influence  upon  science, 
his  youth  and  health  form  a  large  element.  He  has  just  passed  his  forty, 
fifth  year.  If  God  spare  his  life,  truth  can  hardly  fall  to  b«  the  gainer 
from  a  mind  that  is  stored  with  knowledge  of  the  laws  of  the  Creator's 
operations,  and  that  has  learned  to  love  all  beauty  and  hz.lt1  »Cj  rileneas  of 
Nature  and  art. 


SPENCER'S  SYSTEM  OF  PHILOSOPHY. 

THE  PHILOSOPHY  OF  EVOLUTION. 

By  HERBERT  SPENCER. 


Thla  great  system  of  scientific  thought,  the  most  original  and  important  men- 
tal undertaking  of  the  age,  to  which  Mr.  Spencer  has  devoted  his  life,  is  now  well 
advanced,  the  published  volumes  being:  First  Principles,  The  Principles  of  Si- 
tiogy,  two  volumes,  and  The  Principles  of  Psychology,  vol.  i.,  which  will  bo 
shortly  printed. 

This  philosophical  system  differs  from  all  its  predecessors  In  being  solidly 
bi^ed  on  the  sciences  of  observation  and  induction ;  in  representing  the  order 
and  course  of  Nature ;  in  bringing  Nature  and  man,  life,  mind,  and  society,  under 
one  great  law  of  action  ;  and  in  developing  a  method  of  thought  which  may  serve 
for  practical  guidance  in  dealing  with  the  affairs  of  life.  That  Mr.  Spencer  is  the 
man  for  this  great  work  will  be  evident  from  the  following  statements : 

"  The  only  complete  and  systematic  statement  of  the  doctrine  of  Evolution 
with  which  I  am  acquainted  is  that  contained  in  Mr.  Herbert  Spencer's  '  System 
of  Philosophy ; '  a  work  which  should  be  carefully  studied  by  all  who  desire  to 
know  whither  scientific  thought  is  tending."— T.  H.  HUXLEY. 

"  Of  all  our  thinkers,  he  is  the  one  who  has  formed  to  himself  the  largest  new 
scheme  of  a  systematic  philosophy.1' — Prof.  MASSON. 

"  If  any  individual  influence  ift  visibly  encroaching  on  Mills  in  this  country,  it 
is  his."— Ibid. 

"Mr.  Spencer  is  one  of  the  most  vigorous  as  well  as  boldest  '.Linkers  that 
English  speculation  has  yet  produced." — JOIIN  STUART  MILL. 

"  One  of  the  acutest  metaphysicians  of  modern  times."— Ibid. 

"  One  of  our  deepest  thinkers."— Dr.  JOSEPH  D.  HOOKER. 

It  is  questionable  if  any  thinker  of  finer  calibre  has  appeared  ia  our  coua 
try."— GEORGE  HENRY  LEWES. 

"He  alone,  of  all  British  thinkers,  has  organized  a  philosophy."— ffiid. 

"He  is  as  keen  an  analyst  as  is  known  in  the  history  of  philououhy;  I  do  not 
sicept  either  Aristotle  or  Kant." — GEORGE  RIPLEY. 

"  Tf  we  were  to  give  our  own  judgment,  we  should  eay  that,  since  Newton, 
there  has  not  in  England  been  a  philosopher  of  more  remarkable  speculative  and 
tystematizing  talent  than  (in  spite  of  some  errors  and  some  narrowness)  Mr.  Her- 
oert  Spencer."— London  Saturday  Review. 

'•*  We  cannot  refrain  from  offering  our  tribute  of  respect  to  one  who,  whether 
for  the  extent  of  his  positive  knowledge,  or  for  the  profundity  of  his  speculative 
insight,  has  already  achieved  a  name  second  to  none  in  the  whole  range  of  Eng- 
lish philosophy,  and  whose  works  will  worthily  sustain  the  credit  of  EugUefc 
thought  in  the  present  generation."-  Westminster  Eeview. 


rTBRAlTYUTE 

This  book  i,  du.  before  closing  Hm.  on  th.  los.  dole  «™<*4  "dow 

piiFASSTAMPbUbbLOVV 


UNIVERSITY  OF  CALIFORNIA,  BERKELEY 
FORM  NO.  DD6A,  20m,  1  1  /78        BERKELEY,  CA  94720 


" 


763T 


THE  UNIVERSITY  OF  CALIFORNIA  LIBRARY 


